(#587) - add test for open_revs with nonexistent docs
(#587) - fix open_revs for nonexistent doc

By the way: we don't need to fire getRevisionTree if open_revs="all"
so now we don't do it.
Merge pull request #588 from neojski/587-open_revs-nonexistent-doc

587 open revs nonexistent doc