Split rhino and rhino version of lessc.  This lets us have cleaner tests (since we don't need to include the test code in the rhino source).  Also
sets the stage for sharing lessc code between lessc and rhino less (issue #14) and provides a hook so lesscss-java can have custom js.
Merge branch 'rhino-lessc' of https://github.com/dhaber/less.js into dhaber-rhino-lessc