bundle2: add bundle2caps dict on localrepo object

This dictionary will hold bundle2-related capabilities.

mercurial/localrepo.py

@@ -179,6 +179,8 b' class localrepository(object):'
     requirements = ['revlogv1']
     filtername = None
 
+    bundle2caps = {'HG20': ()}
+
     # a list of (ui, featureset) functions.
     # only functions defined in module of enabled extensions are invoked
     featuresetupfuncs = set()