allow use of extensions in python hooks
extensions are loaded with hgext_ prefix, try to use them if
the module is not found in the normal path
# 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