iequivalent-class? now works correctly.

Previously it was checking to see if a class was equivalent
to itself so always returning true.
Support for caching namespace lookup.

This was happening multiple times for any render which was pretty slow. Now
using dynamic binding of a cache value to avoid this. Laziness has been
removed as this circumvents the dynamic binding. Added a "resolve-symbol"
method into lookup as it is more generally useful.