exchange: split between modern and legacy code We make it clearer what code is old crust and what code is the cutting edge part.

push: add extra warning about pushing to old server Pushing using old method is slow and racy. We adds warning to point this to the user. We also add inline comment to clarify the function purpose.

push: exit obsexchange early if disabled We were exiting the function later, in particular -after- issuing a message about exchanging obsmarkers.

compat: drop special code handling change in push/pull op API All version of Mercurial we support have the same API.

discovery: split discovery related code in 'obsdiscovery' More code splitting for more clarity.

exchange: rename the module Let's add a 'obs' prefix to make the module role clearer.

setup.py: include all evolve submodule We are splitting more and more code into submodule, we make sure their are properly installed. As a side effect the 'legacy' module is now installed, that is not too important. The 'evolve.hack' package is still non installed by default, as intended.