manifestctx: add _revlog() function
The `self._repo.manifestlog._revlog` code is getting copy and pasted a lot in
manifestctx. Let's make it a function so it can be reused. This will make future
patches cleaner too.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See https://mercurial-scm.org/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.