Add go-wrapper support for Go 1.4 Custom Import Paths, relegating .godir support legacy and "second fiddle"

Fixes #29

I haven't run `update.sh` yet in the spirit of making this easier to review. :+1:
I find the cat version easier to read, what about merging the two in:
goDir="$(go list -e -f '{{.ImportComment}}' 2>/dev/null || cat .godir 2>/dev/null)"