localrepo: rename in-memory tag cache instance attributes (
issue548).
- self.tagscache to self._tags
- self._tagstypecache to self._tagtypes
- this is for consistency, readability, privacy, and to subtly hint
that "caching" is something else
adding a/b/c/d/x
adding a/b/c/d/y
adding a/b/c/d/z
moving a/b/c/d/x to z/b/c/d/x
moving a/b/c/d/y to z/b/c/d/y
moving a/b/c/d/z to z/b/c/d/z