copies: teach symmetric difference about working revisions
- use changelog.count() as a pseudo revision number
- abort early in copies if revs are the same
- eliminate working dir hacks in copies
- yield results as they're found
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.