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:
On Go 1.3 and lower, it returns non-zero because "ImportComment" doesn't
exist (hence the "2>/dev/null" and the "|| true"), but on Go 1.4, it
returns successfully because the "ImportComment" field exists in the
struct, but is empty, so it just has no output.