query engine cache alterations

- new metric that tries to measure directory evictions. ie. engines
that are removed from the cache to make room for a different
directory as opposed to being refreshed
- pulled a few anonymous inner classes up to top level and put them
with their friends in a new subpackage called 'engine'
- slightly nicer test code
- less static logic
minor formatting changes
change minor test log labeling
possibly less confusing engine chache metric names
Merge pull request #46 from addthis/engine-cache-changes

Engine cache changes