don't use hasattr in repo.invalidate
hasattr ends up calling __getattr__ which will instantiate the very
attributes we want to remove.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
See http://www.selenic.com/mercurial/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.