subrepo: abort instead of pushing/pulling to the repo itself
_abssource will now abort (or return None) in the rare cases where no push/pull
path can be found.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.