MQ: tidy up if a qpush is interrupted.
This aborts the transaction, makes sure the dirtied dirstate isn't
written out, and cleans up the working directory.
adding dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)