localrepo: rename proxycls to filteredrepo

localrepo: rename proxycls to filteredrepo

When debugging in a Python shell, the type of "repo" is "proxycls", which
could confuse new people.

    In [1]: repo
    Out[1]: <mercurial.localrepo.proxycls at 0x7f65d4b976d0>

Let's rename it to "filteredrepo" to make it clearer.

--- a/mercurial/localrepo.py	Wed Mar 08 17:35:20 2017 -0800
+++ b/mercurial/localrepo.py	Thu Mar 09 15:10:27 2017 -0800
@@ -484,9 +484,9 @@
         """Return a filtered version of a repository"""
         # build a new class with the mixin and the current class
         # (possibly subclass of the repo)
-        class proxycls(repoview.repoview, self.unfiltered().__class__):
+        class filteredrepo(repoview.repoview, self.unfiltered().__class__):
             pass
-        return proxycls(self, name)
+        return filteredrepo(self, name)
 
     @repofilecache('bookmarks', 'bookmarks.current')
     def _bookmarks(self):