manifest: move revlog specific options from manifest to manifestrevlog
The manifestv2 and treeondisk options are specific to how we serialize the
manifest into revlogs, so let's move them onto the manifestrevlog class. This
will allow us to add a manifestlog.add() function in a future diff that will
rely on manifestrevlog to make decisions about how to serialize the given
manifest to disk.
We have to move a little bit of extra logic about the 'dir' as well, since it is
used in conjunction with the treeondisk option to decide the revlog file name.
It's probably good to move this down to the manifestrevlog class anyway, since
it's specific to the revlog.
(binary:application/octet-stream)