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.

manifest: adds manifestctx.readfast This adds a copy of manifest.readfast to manifestctx.readfast and adds a consumer of it. It currently looks like duplicate code, but a future patch causes these functions to diverge as tree concepts are added to the tree version.

manifest: add manifestctx.readdelta() This adds an implementation of readdelta to the new manifestctx class and adds a couple consumers of it. This currently appears to have some duplicate code, but future patches cause this function to diverge when things like "shallow" are introduced.

merge with stable