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.
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)