Fixed #6195 -- Documented caching options for javascript_catalog.
Fixed #19634 -- Added proper __hash__ methods.

Classes overriding __eq__ need a __hash__ such that equal objects have
the same hash.

Thanks akaariai for the report and regebro for the patch.
Fixed #18191 -- Don't consider Accept-Language redundantly in cache key.

Thanks to choongmin for the original patch.
Fixed a caching test on Python 3.
Updated an inaccurate comment.

Tests can run nearly as fast under PostgreSQL and MySQL as under SQLite
with a bit of configuration and the speedup is always a good thing.