revset: changed generatorset code to remove unnecesary function call
Removed _nextitem() method, now __iter__ has that logic and __contains__ uses
__iter__ to check for membership.
$ 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