Summary:
Before, the Interprocedural functor was a bit inflexible. You couldn't do custom postprocessing like normalizing the post state or coverting the post from an astate type to a summary type.
Now, you can do whatever you want by passing a custom `~compute_post` function.
Since `AbstractInterpreter.compute_post` can be used by clients who don't care to do anything custom, this doesn't create too much boilerplate.
Reviewed By: jvillard
Differential Revision: D4309877
fbshipit-source-id: 8d1d85d