py3: convert opts keys to bytes using pycompat.byteskwargs()
This fixes the py3 build broken due to
56b2074114b19e12abd9cd4c378d58b702232705.
Differential Revision: https://phab.mercurial-scm.org/D3853
revset: leverage orset() to flatten ancestor() arguments
This also makes orset() accept an empty argument because nullary ancestor()
call is valid. That's not the case for orset(), but should be okay.
grep: deprecates `--all` flag
As the name "all" is a misnomer for an option that searches on diffs of revisions,
we are moving to diff flag from all, deprecating it in the process.
Differential Revision: https://phab.mercurial-scm.org/D3825