memctx: remove __nonzero__ since it is now inherited

memctx: remove __int__ since it is now inherited

memctx: remove __str__ since it is now inherited

memctx: call super.__init__ instead of duplicating code

memctx: inherit from committablectx This patch marks the start of having memctx inherit from committablectx, thereby making it a full-fledged context that will eventually grow the ability to perform diffing and also merging.

committablectx: fix _manifest doc string

context: fix wrong indentation from renaming method

push: use bundle2 to push phases when available We now use a bundle2 container to push all phase updates at the same time. This is a significant step forward, even if further refactoring is needed to unify phase push with the changeset push.

pushkey: add an ``encode`` function This function is just a shorthand for ``encoding.fromlocal``. It will help hiding the encoding business from other code exchanging pushkey data over the wire.

bundle2: add ``pushkey`` support After ``listkeys`` we can now include ``pushkey`` request in a bundle2. The part uses a very simple scheme closest as possible to the current wireproto command for ``pushkey``. We may eventually decide for a more sophisticated part format before the protocol becomes final.