changegroup: add source parameter to generatemanifests Extensions, like remotefilelog, will want to look at the source of a pull when determining what manifests to add to a changegroup. For instance, on push they will include everything, while on pull they won't. Differential Revision: https://phab.mercurial-scm.org/D686

changegroup: remove changegroup dependency from revlog.addgroup Previously revlog.addgroup would accept a changegroup and a linkmapper and use it to iterate of the deltas. As part of untangling the revlog-changegroup interdependency, let's move the changegroup delta iteration logic to it's own function and pass the simple iterator to the revlog instead. This will make it easier to introduce non-revlogs stores in the future, without reinventing any changegroup specific logic. Differential Revision: https://phab.mercurial-scm.org/D688