Fix an inverted conditional that was mistakenly inverted in the move to FailoverLoader and no reflection.
Add a proper test for FailoverLoader.
Rename TestOnlyModuleAdapter -> TestingModuleAdapter to line it up with TestingLoader.
Merge pull request #290 from cgruber/handleabstractparents

Fix conditional that was inadvertently inverted in the FailoverLoader re-work.
Create a cache for class loading that both successfully loaded classes, as well as class lookup failures (using Void.class as a null object).

This change also reworks the loading infrastructure to not throw/catch class cast exceptions since we expect cache misses in certain cases, and we want fast response to multiple lookups.  It also turns Loader into an abstract class, vs. an interface.
Make cache private - no access needed for testing.
Merge pull request #292 from cgruber/cacheclassloading

Create a cache for class loading