merge: add commands.merge.require-rev to require an argument to hg merge
This is related to commands.rebase.requiredest, commands.update.requiredest, and
commands.push.require-revs. Since it isn't really a "destination", I went with
require-rev to be similar to push's require-revs.
Differential Revision: https://phab.mercurial-scm.org/D7620
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.