Support the JDK JavaCompiler too (next to Eclipse and Janino)

Since java 6, there's an API to use the JDK compiler, so we can support it, next to Eclipse and Janino.
The JDK compiler has the reputation of being faster these days. Also, since the drools classes are JDK compiled and the runtime is usually JDK, this might also result into faster code.

Here's a howto:
http://www.dzone.com/links/r/generating_java_classes_dynamically_through_java.html