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.
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory