phases: fix phase synchronization on push The bugs seemed to show up when element not in future common changeset should hold new hold phase data. The whole phase push machinery was rewritten in the process.

phases: implements simple revset symbol This changeset adds ``public()``, ``draft()`` and ``secret`` symbol for revset.

phases: store phase values in constant instead of using raw integer Phases constant are named after the phase name. Usage of integer have been replaced by proper constant.