localrepo: move filtername to __init__

This is obviously an instance attribute, not a type attribute. The
modern Python style is to use __init__ for defining these.

This exposes statichttprepo as inheriting from localrepository
without calling its __init__. As a result, its __init__ defines
a lot of variables that methods on localrepository's methods need.
But factoring the common bits into a separate class is for another
day.

mercurial/localrepo.py

@@ -270,7 +270,6 b' class localrepository(object):'
         'treemanifest',
         'manifestv2',
     }
-    filtername = None
 
     # a list of (ui, featureset) functions.
     # only functions defined in module of enabled extensions are invoked
@@ -278,6 +277,7 b' class localrepository(object):'
 
     def __init__(self, baseui, path, create=False):
         self.requirements = set()
+        self.filtername = None
         # wvfs: rooted at the repository root, used to access the working copy
         self.wvfs = vfsmod.vfs(path, expandpath=True, realpath=True)
         # vfs: rooted at .hg, used to access repo files outside of .hg/store

mercurial/statichttprepo.py

@@ -127,6 +127,7 b' class statichttprepository(localrepo.loc'
         self._phasedefaults = []
 
         self.names = namespaces.namespaces()
+        self.filtername = None
 
         try:
             requirements = scmutil.readrequires(self.vfs, self.supported)