patch: generalize the use of patchmeta in applydiff() - Add patchmeta.copy() and emit copies from iterhunks. Modifying patchmeta instances in applydiff() makes things simpler. - Rename selectfile() into makepatchmeta(). It is responsible for creating patchmeta for regular patches. - Pass patchmeta objects to patchfile() directly patchmeta instances were associated with git patches, for regular patches we had to pass additional variables to tell the patch intent to patchfile(). Instead, we generate patchmeta for regular patches and pass them. This will also help with patch filtering by matcher objects.

patch: stop updating changed files set in applydiff() This information is more correctly returned by backends. The extra updated file removed from test-mq-merge.t output came from changes from git patches being counted before being really applied in some cases.

patch: turn patch() touched files dict into a set