Add funcQueue to Gravy

Review Request #635 — Created Nov. 14, 2008 and submitted

Navi (deprecated)
This adds a funcQueue utility function to djblets.gravy. The purpose of this is to queue up several functions, allowing them to operate one at a time. It is up to the functions to invoke the function to invoke the next function in the list.

This is useful for chaining ajax calls so only one operates at a time. It is intentionally very simple.
Works fine with my corresponding change in Review Board.