patch: use field names instead of field numbers on scmutil.status
As part of my pytype adventures I want to make scmutil.status no longer a
subclass of tuple. This is part of that process.
Differential Revision: https://phab.mercurial-scm.org/D7401
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state