hidden: move hiddenrevs set on the repository
This set is always accessed through the repo for now. Having this set
carried by the changelog make it complicated to:
- initialize it, computing hidden set may involve revset call
- lazy compute it, (1) only the changelog can detect someone access it,
(2) only the repo have enought knowledge to compute it.
In later version I expect he changelog to apply filtering itself and the set to
be carried by changelog again.
$ 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