Path elements in JSON output are not consistent between runs

I'm using capslock (probably in a way that is not intended) to identify module wide imports that are org-foreign. This is a cheap hack implemented [here](https://github.com/efd6/cl) with obvious issues of false positives.

One of the extensions that I was interested in making was to use the path output to identify specific syscalls that are made when a CAPABILITY_SYSTEM_CALLS is fount. This requires examining the call path array in the capslock JSON output so that the AST of the package can be examined for the actual args of the sycall call. While looking into this, I found that the order of the input packages to capslock impacts on the output of the JSON and the final sites identified in the path are not stable between runs (the summary output and caps counts *are* stable).

To demonstrate this here are example runs of capslock with a post processor available here https://play.golang.com/p/JoC-mB_NZYA (built as an executable `syscalls`). The tests were run in packetbeat/protos directory of http://github.com/elastic/beats.

Different packages order (note missing `unix.CmsgSpace` callsite is consistent between runs):
```
$ capslock -goos darwin -goarch amd64 -output json -packages github.com/insomniacslk/dhcp/dhcpv4,github.com/miekg/dns 2>/dev/null | syscalls
syscall.Bind: {{Name:github.com/insomniacslk/dhcp/dhcpv4.MakeListeningSocket Site:{Filename:client.go Line:113 Column:23}}}
syscall.Sendto: {{Name:github.com/insomniacslk/dhcp/dhcpv4.BroadcastSendReceive Site:{Filename:client.go Line:213 Column:25}}}
syscall.SetsockoptInt: {{Name:github.com/insomniacslk/dhcp/dhcpv4.BindToInterface Site:{Filename:bindtodevice_darwin.go Line:15 Column:30}}, {Name:github.com/insomniacslk/dhcp/dhcpv4.MakeBroadcastSocket Site:{Filename:client.go Line:81 Column:29}}}
$ capslock -goos darwin -goarch amd64 -output json -packages github.com/miekg/dns,github.com/insomniacslk/dhcp/dhcpv4 2>/dev/null | syscalls
golang.org/x/sys/unix.CmsgLen: {{Name:golang.org/x/net/internal/socket.controlHeaderLen Site:{Filename:cmsghdr_unix.go Line:13 Column:21}}}
golang.org/x/sys/unix.CmsgSpace: {{Name:golang.org/x/net/internal/socket.controlMessageSpace Site:{Filename:cmsghdr_unix.go Line:21 Column:23}}}
golang.org/x/sys/unix.SetsockoptInt: {{Name:github.com/miekg/dns.reuseportControl$1 Site:{Filename:listen_reuseport.go Line:19 Column:29}}}
syscall.Bind: {{Name:github.com/insomniacslk/dhcp/dhcpv4.MakeListeningSocket Site:{Filename:ipsock.go Line:180 Column:2}}}
syscall.Sendto: {{Name:github.com/insomniacslk/dhcp/dhcpv4.BroadcastSendReceive Site:{Filename:ipsock.go Line:278 Column:35}}}
syscall.SetsockoptInt: {{Name:github.com/insomniacslk/dhcp/dhcpv4.BindToInterface Site:{Filename:ipsock.go Line:296 Column:42}}, {Name:github.com/insomniacslk/dhcp/dhcpv4.MakeBroadcastSocket Site:{Filename:ipsock.go Line:151 Column:19}}}
```

Single package, multiple runs:
```
$ capslock -goos darwin -goarch amd64 -output json -packages github.com/miekg/dns 2>/dev/null | syscalls
golang.org/x/sys/unix.CmsgLen: {{Name:golang.org/x/net/internal/socket.controlHeaderLen Site:{Filename:cmsghdr_unix.go Line:13 Column:21}}}
golang.org/x/sys/unix.CmsgSpace: {{Name:golang.org/x/net/internal/socket.controlMessageSpace Site:{Filename:cmsghdr_unix.go Line:21 Column:23}}}
golang.org/x/sys/unix.SetsockoptInt: {{Name:github.com/miekg/dns.reuseportControl$1 Site:{Filename:listen_reuseport.go Line:19 Column:29}}}
$ capslock -goos darwin -goarch amd64 -output json -packages github.com/miekg/dns 2>/dev/null | syscalls
golang.org/x/sys/unix.CmsgLen: {{Name:golang.org/x/net/internal/socket.controlHeaderLen Site:{Filename:cmsghdr_unix.go Line:13 Column:21}}}
golang.org/x/sys/unix.CmsgSpace: {{Name:golang.org/x/net/internal/socket.controlMessageSpace Site:{Filename:cmsghdr_unix.go Line:21 Column:23}}}
golang.org/x/sys/unix.SetsockoptInt: {{Name:github.com/miekg/dns.reuseportControl$1 Site:{Filename:listen_reuseport.go Line:19 Column:29}}}
```