tests/test-status-inprocess.py.out

bundle2.processbundle: let callers request default behavior

This patch series is intended to allow bundle2 push reply part handlers to
make changes to the local repository; it has been developed in parallel with
an extension that allows the server to rebase incoming changesets while applying
them.

The default transaction getter for processbundle is a private function that
raises an exception; this diff lets calling code pass None as the transaction
getter to explicitly request this default behavior.

The next diff will check a config option to determine whether to provide a
transaction to the reply bundle processor.  If one shouldn't be provided, the
code needs a way to specify that the default behavior should be used.

% creating repo
% add and commit
C test.py
% change
M test.py