tests/test-mq-qsave.t

revset: extend fullreposet to make "null" revision magically appears in set

As per fullreposet.__and__, it can omit the range check of rev.  Therefore,
"null" revision is accepted automagically.

It seems this can fix many query results involving null symbol.  Originally,
the simplest "(null)" query did fail if there were hidden revisions.  Tests
are randomly chosen.

fullreposet mimics the behavior of localrepo, where "null" revision is not
listed but contained.

  $ 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