pull: make discovery phase extensible
We apply the same approach as for push and make the discovery extensible. There
is only one user in core right now, but we already know we'll need something
smarter for obsmarkers. In fact the evolve extension could use this to cleanly
extend discovery.
The main motivation for this change is consistency between push and pull.
Mercurial
=========
Mercurial is a fast, easy to use, distributed revision control tool
for software developers.
Basic install:
$ make # see install targets
$ make install # do a system-wide install
$ hg debuginstall # sanity-check setup
$ hg # see help
Running without installing:
$ make local # build for inplace usage
$ ./hg --version # should show the latest version
See http://mercurial.selenic.com/ for detailed installation
instructions, platform-specific notes, and Mercurial user information.