DRILL-1155: Add option to use JDK compiler and use it for runtime generated code over a certain threshold
+ Updating Janino to 2.7.4 (from 2.6.1).
+ Added session options `exec.java_compiler`:[DEFAULT, JDK, JANINO] and `exec.java_compiler_janino_maxsize`(256k).
+ Fix a bug in FragmentExecutor.java(125) where the root operator is not stopped in case of fragment failure.
+ Print Java stack trace of the allocator code if a TLA detects that any of the ChildAllocator is not closed.
