remote-hg: do not interfer with hg's revs() method

remote-hg: do not interfer with hg's revs() method

Matt Mackall introduced a revs() method to the localrepo class on Wed
Nov 2 13:37:34 2011 in the commit 'localrepo: add revs helper method'.
It is used when constructing a commit in memory.

If we store the set of revs we want to handle under the same name, it
overrides that method, resulting in an unpleasant 'TypeError: 'set'
object is not callable' whenever we want to push (as we are constructing
commits in memory, then).

So let's work around that by renaming our field to 'revs_' and hope that
upstream Mercurial does not introduce a field of that name, too.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>