largefiles: avoid match.files() in conditions
See 9789b4a7c595 (match: introduce boolean prefix() method,
2014-10-28) for reasons to avoid match.files() in conditions.
$ 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