phases: fix performance regression with Python 2
Unlike Python 3, xrange doesn't support efficient "in" and uses a linear
time scan instead. Expand the condition to handle it fast.
Differential Revision: https://phab.mercurial-scm.org/D9072
$ 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