make incoming work via ssh (issue139); move chunk code into separate module. Incoming ssh needs to detect the end of the changegroup, otherwise it would block trying to read from the ssh pipe. This is done by parsing the changegroup chunks. bundlerepo.getchunk() already is identical to localrepo.addchangegroup.getchunk(), which is followed by getgroup which looks much like what you can re-use in bundlerepository.__init__() and in write_bundle(). bundlerevlog.__init__.genchunk() looks very similar, too, as do some while loops in localrepo.py. Applied patch from Benoit Boissinot to move duplicate/related code to mercurial/changegroup.py and use this to fix incoming ssh.

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