rebase: don't mark file as removed if missing in parent's manifest (
issue2725)
tags: no need to check for valid nodes
_findtags in localrepo checks that nodes exist in the revlog so we
can't get a LookupError here.
The output of 'hg tags' stays the same since tags to unknown nodes
didn't get printed before anyway due to
ae3089cefaab.
localrepo: ignore tags to unknown nodes (
issue2750)