fix the cat command
- improve localrepo.walk when passed a node
- make the differents walk commands in commands.py accept a node
- change commands.cat to walk over a revision
- add a test
# 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