scmutil: rename classes from "opener" to "vfs" For backwards compatibility, aliases for the old names are added, except for "abstractopener", "statichttpopener" and "_fncacheopener", because these are not used in Mercurial core implementation after this patch. "_fncacheopener" was only referred in "fncachestore" constructor, so this patch also renames from "_fncacheopener" to "_fncachevfs" there.