Add revlog.strip to truncate away revisions.
This updates the revlog data structures for index and nodemap in place
so the .d and .i files don't need to be reread after stripping away a revision.
# repo.py - repository base classes for mercurial
#
# Copyright 2005 Matt Mackall <mpm@selenic.com>
#
# This software may be used and distributed according to the terms
# of the GNU General Public License, incorporated herein by reference.
class RepoError(Exception): pass