Use Class#isAssignableFrom instead of string comparisons for instanceof.

This catches super classes, abstract classes and interfaces as well.
Clean up detritus
add JIT threshold setting
introduce IR’s JITCompiler
add wiring for JITting code in the background

heavily inspired on JRuby’s InterpretedIRMethod
split JIT and compile modes
compiled functions inherit from AbstractFunction
interesting testcase :) (TO BE NUKED)
ignore this JIT test during travis runs