convert: activate subversion engine
Fail gracefully if the subversion python bindings are not installed.
Support --rev option to convert as well as URL@rev.
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.