[PATCH V2] localrepo: cache types for filtered repos (issue5043)

[Jun Wu]

Excerpts from Gregory Szorc's message of 2017-07-03 08:30:10 -0700:
> > I think this may still leak a proxy class in hgweb-type applications. Do
> > we need a type object per repository instance?
> 
> I don't follow. Where's the leak?
> 
> If you are proposing a module-level cache, I *think* that will work. As
> long as weak refs are used, cache entries should go away when the last
> underlying repo referencing them does.

I think module-level is better. I tried to express that in comments for V1
but it might be unclear at that time.  Since we only have limited (4?)
filters, weakref could be optional.