peer: introduce real peer classes This change separates peer implementations from the repository implementation. localpeer currently is a simple pass-through to localrepository, except for legacy calls, which have already been removed from localpeer. This ensures that the local client code only uses the most modern peer API when talking to local repos. Peers have a .local() method which returns either None or the underlying localrepository (or descendant thereof). Repos have a .peer() method to return a freshly constructed localpeer. The latter is used by hg.peer(), and also to allow folks to pass either a peer or a repo to some generic helper methods. We might want to get rid of .peer() eventually. The only user of locallegacypeer is debugdiscovery, which uses it to pose as a pre-setdiscovery client. But we decided to leave the old API defined in locallegacypeer for clarity and maybe for other uses in the future. It might be nice to actually define the peer API directly in peer.py as stub methods. One problem there is, however, that localpeer implements lock/addchangegroup, whereas the true remote peers implement unbundle. It might be desireable to get rid of this distinction eventually.