sidedata: add a debugsidedata command
The command provide basic capabilities to inspect revision side data.
Differential Revision: https://phab.mercurial-scm.org/D6897
sidedata: test we can successfully write sidedata
For now we just write them and rejoice on the lack of crashes.
Differential Revision: https://phab.mercurial-scm.org/D6896
sidedata: make sure we don't use the flag if there are not sidedata
Ensuring this at this level seems safer than relying on caller doing the right
thing.
G: changed mercurial/revlog.py
Differential Revision: https://phab.mercurial-scm.org/D6895