[MERGE] Add wrapper function for lazily registering filter stack maps.

[Ian Clatworthy]

John Arbash Meinel wrote:

> hmm... my preference is actually the opposite. By writing decorator
> functions, you end up re-implementing all the functions you need on the
> registry, just to have them call into the registry.
> 
> Is there a reason you think a registry isn't a proper api for what you need?

No big reason - mainly abstraction and the ability to add extra stuff
if required. Currently, the only extra stuff is some explicit error
checking for duplicates (which might even be handled at the layer below?).

Ian C.