revset: use _generatorset directly in _revdescendant
_ascgeneratorset is going away.
http://mercurial.selenic.com/bts/issue1089 $ hg init $ mkdir a $ echo a > a/b $ hg ci -Am m adding a/b $ hg rm a removing a/b (glob) $ hg ci -m m a $ mkdir a b $ echo a > a/b $ hg ci -Am m adding a/b $ hg rm a removing a/b (glob) $ cd bRelative delete: $ hg ci -m m ../a $ cd ..