Resolve symlinks in GetRepoImportPath.
Resolve symlinks in GetRepoImportPath.

An entry in $GOPATH might be a symlink, while the path to the repository
is not, which made detecting the actual import path impossible.

By following both the repoPath and the srcRoot as symlinks, we should
end up with two paths that have a common prefix, the perceived GOPATH.

shurcooL/go