Cache looked up methods

Should improve invokeinterface speeds.
Math for pow. Add more later
findObjectField is now getObjectField

Seems more appropriate
Show some useful error info
Fix silly bug with virtuals

Virtual methods are most often called by the index which is located at
compile time, rather than runtime like interfaces. Therefore return
index when possible
Added Class

No pun intended. Lots of things make use of this in rt.jar, and some of
them we'd like to mimic.