Fixes for version information for modules (re-submit)

Created originally on Bitbucket by ayshih (Albert Shih)

Was already merged in Bitbucket before import, marked as merged by the import user

• Fixed hgstamp generation so that it is actually updated when necessary (before, the file needed to be deleted)
• Fixed searching for the most recent relevant commit (e.g., for module strings) so that only ancestors are looked at, rather than commits across all branches, which was misleading