shelve: do not add the dirstate backup to the transaction
Otherwise the transaction will properly clean up its mess on abort… deleting the
backup in the process.
This break with dirstate-v2 that has more file than just the dirstate. The
dirstate itself is full of various exception and is "fine" when using
dirstate-v1.
#require docutils gettext
$ $TESTDIR/check-gendoc el
checking for parse errors