Using rice.Config rice tool can't find calls

Nobody has claimed this yet.

Based on the example.go file

``` go
package main

import (
"fmt"
"github.com/gutenye/go.rice"
)

func main() {
r := rice.Config{
LocateOrder: []rice.LocateMethod{rice.LocateFS, rice.LocateEmbedded},
}

_, _ = r.FindBox("www")
}
```

run `$GOPATH/bin/rice -v embed-go`

```
2015/05/14 10:21:19 using pwd as import path
2015/05/14 10:21:19 using import paths: [gothing]
2015/05/14 10:21:19 scanning file "/Development/Go/gothing/src/gothing/main.go"
no calls to rice.FindBox() found
2015/05/14 10:21:19
2015/05/14 10:21:19 rice finished successfully
```

Start with the example.go reproduction and run `$GOPATH/bin/rice -v embed-go` to confirm the “no calls to rice.FindBox() found” output. Trace the embed-go call scanner from that command and determine why the rice.Config-based FindBox call is missed; done means the command detects the call and processes the www box.

Written by the indexing model from the issue text.