Treescript

Changed
- Use mozilla-version to ensure new Fennec versions are supported

Added
- Allowed Fennec beta/release version files

Fixed
- Update hg.mozilla.org fingerprint ([Bug 1495464](https://bugzilla.mozilla.org/show_bug.cgi?id=1495464))

Fixed
- Update robustcheckout to a version supporting mercurial 4.7.1.

Fixed
- Backed out PR 54 for bustage when the version bump has already happened (PR 69)

Added
- Sanity check that we are pushing the right number of commits. (PR 54)
- Updated robustcheckout from upstream (PR 58)
- Support for pushing with DONTBUILD contributed by rahul-shiv (PR 59)