godebug does not work with code that imports net/http (since go 1.6)

Nobody has claimed this yet.

whenever I import `net/http`, I get all sorts of errors when I try and run `godebug`. The same code works fine when I build and run it with go directly.

Here is a simple example app and the output of go debug....

```
$cat main.go
package main

import (
"net/http"
)

func HandleIndex(w http.ResponseWriter, r *http.Request) {
// io.WriteString(w, "hello, world\n")
}

func main() {

_ = "breakpoint"

http.HandleFunc("/", HandleIndex)

}
```

```
$godebug run main.go
/usr/local/go/src/net/interface_bsd.go:12:2: could not import golang_org/x/net/route (cannot find package "golang_org/x/net/route" in any of:
/usr/local/go/src/golang_org/x/net/route (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/route (from $GOPATH))
/usr/local/go/src/net/interface_darwin.go:10:2: could not import golang_org/x/net/route (cannot find package "golang_org/x/net/route" in any of:
/usr/local/go/src/golang_org/x/net/route (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/route (from $GOPATH))
/usr/local/go/src/net/interface_darwin.go:13:40: undeclared name: route
/usr/local/go/src/net/interface_darwin.go:14:14: undeclared name: route
/usr/local/go/src/net/interface_darwin.go:18:9: undeclared name: route
/usr/local/go/src/net/interface_darwin.go:24:14: undeclared name: route
/usr/local/go/src/net/interface_darwin.go:28:15: undeclared name: route
/usr/local/go/src/net/http/h2_bundle.go:45:2: could not import golang_org/x/net/http2/hpack (cannot find package "golang_org/x/net/http2/hpack" in any of:
/usr/local/go/src/golang_org/x/net/http2/hpack (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/http2/hpack (from $GOPATH))
/usr/local/go/src/net/http/h2_bundle.go:46:2: could not import golang_org/x/net/lex/httplex (cannot find package "golang_org/x/net/lex/httplex" in any of:
/usr/local/go/src/golang_org/x/net/lex/httplex (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/lex/httplex (from $GOPATH))
/usr/local/go/src/net/http/http.go:10:2: could not import golang_org/x/net/lex/httplex (cannot find package "golang_org/x/net/lex/httplex" in any of:
/usr/local/go/src/golang_org/x/net/lex/httplex (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/lex/httplex (from $GOPATH))
/usr/local/go/src/net/http/server.go:31:2: could not import golang_org/x/net/lex/httplex (cannot find package "golang_org/x/net/lex/httplex" in any of:
/usr/local/go/src/golang_org/x/net/lex/httplex (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/lex/httplex (from $GOPATH))
/usr/local/go/src/net/http/transfer.go:21:2: could not import golang_org/x/net/lex/httplex (cannot find package "golang_org/x/net/lex/httplex" in any of:
/usr/local/go/src/golang_org/x/net/lex/httplex (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/lex/httplex (from $GOPATH))
/usr/local/go/src/net/http/transport.go:30:2: could not import golang_org/x/net/lex/httplex (cannot find package "golang_org/x/net/lex/httplex" in any of:
/usr/local/go/src/golang_org/x/net/lex/httplex (from $GOROOT)
/Users/anuaimi/code/go/src/golang_org/x/net/lex/httplex (from $GOPATH))
/usr/local/go/src/net/http/h2_bundle.go:848:19: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:1827:11: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:1851:52: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:1862:51: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:5020:11: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:6735:20: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:3131:18: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:3187:46: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:6834:22: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:6926:30: undeclared name: hpack
/usr/local/go/src/net/http/transport.go:323:8: undeclared name: httplex
/usr/local/go/src/net/http/transport.go:327:9: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:5287:26: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:5290:12: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:6659:4: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:1920:2: invalid operation: hdec (variable of type *invalid type) has no field or method SetEmitEnabled
/usr/local/go/src/net/http/h2_bundle.go:1921:2: invalid operation: hdec (variable of type *invalid type) has no field or method SetMaxStringLength
/usr/local/go/src/net/http/h2_bundle.go:1922:2: invalid operation: hdec (variable of type *invalid type) has no field or method SetEmitFunc
/usr/local/go/src/net/http/h2_bundle.go:1922:27: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:1926:7: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:1942:4: invalid operation: hdec (variable of type *invalid type) has no field or method SetEmitEnabled
/usr/local/go/src/net/http/h2_bundle.go:1948:4: invalid operation: hdec (variable of type *invalid type) has no field or method SetEmitEnabled
/usr/local/go/src/net/http/h2_bundle.go:1957:8: invalid operation: hdec (variable of type *invalid type) has no field or method SetEmitFunc
/usr/local/go/src/net/http/h2_bundle.go:1957:33: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:1962:16: invalid operation: hdec (variable of type *invalid type) has no field or method Write
/usr/local/go/src/net/http/h2_bundle.go:1979:12: invalid operation: hdec (variable of type *invalid type) has no field or method Close
/usr/local/go/src/net/http/h2_bundle.go:5797:7: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:5801:8: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:5892:2: invalid operation: cc.henc (variable of type *invalid type) has no field or method WriteField
/usr/local/go/src/net/http/h2_bundle.go:5892:21: undeclared name: hpack
/usr/local/go/src/net/http/server.go:789:25: undeclared name: httplex
/usr/local/go/src/net/http/server.go:793:7: undeclared name: httplex
/usr/local/go/src/net/http/server.go:797:8: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:2517:7: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:3042:20: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:3045:23: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:3899:3: invalid operation: sc.hpackEncoder (variable of type *invalid type) has no field or method SetMaxDynamicTableSize
/usr/local/go/src/net/http/h2_bundle.go:6711:22: undeclared name: httplex
/usr/local/go/src/net/http/h2_bundle.go:6838:2: invalid operation: enc (variable of type *invalid type) has no field or method WriteField
/usr/local/go/src/net/http/h2_bundle.go:6838:17: undeclared name: hpack
/usr/local/go/src/net/http/h2_bundle.go:6942:8: undeclared name: httplex
/usr/local/go/src/net/http/http.go:42:10: undeclared name: httplex
/usr/local/go/src/net/http/transfer.go:566:14: undeclared name: httplex
/usr/local/go/src/net/http/transfer.go:568:23: undeclared name: httplex
couldn't load packages due to errors: net/http, net
```

Start by reproducing the report with the provided main.go and `godebug run main.go`, then compare it with building and running the same program using Go directly. Investigate godebug's handling of the Go 1.6 `net/http` dependencies shown in the output; done means the example runs under godebug without the reported import errors.

Written by the indexing model from the issue text.