store: rename field name from "opener" to "vfs" in internal classes for fncache These fields are used only in store module, so keeping "self.opener" for backward compatibility like as "localrepository" class is not needed.

store: rename argument name from "op"(ener) to "vfs"

verify: rename "hasmanifest" variable for source code readability Before this patch, there are two ambiguous variables: "havemf" and "hasmanifest". "havemf" means whether there are any "manifest" entries. "hasmanifest" means whether there are any "changelog" entries referring to "manifest" entry. This patch renames from "hasmanifest" to "refersmf" to clear difference from "havemf".