revlog: add a `get_revlog` method
This might seen weird, but I actually thing we have been needing this for a
long time. There is multiple object that kind of pretend being revlogs while
actually wrapping the actual revlog. Since multiple code needs to access the
actuel revlog. See documentation for more details.
Expect cleanup of various places one the current series is done.
#require docutils gettext
$ $TESTDIR/check-gendoc da
checking for parse errors