largefiles: quiet (and document) undefined name errors (issue3886)

These names were found using Cython; I was completely puzzled until
I searched the rest of the tree. It's icky to mess with another
module's namespace, but ickier yet to do so without a comment :-)

hgext/largefiles/proto.py

@@ -16,6 +16,11 b" LARGEFILES_REQUIRED_MSG = ('\\nThis repos"
                            '\n\nPlease enable it in your Mercurial config '
                            'file.\n')
 
+# these will all be replaced by largefiles.uisetup
+capabilitiesorig = None
+ssholdcallstream = None
+httpoldcallstream = None
+
 def putlfile(repo, proto, sha):
     '''Put a largefile into a repository's local store and into the
     user cache.'''