Add new jythonlib module to support libraries in stdlib that are
written in Python (examples: _socket, threading) that need more
precise integration from Java and Jython's runtime.

For now, this includes building dicts with arbitrary ConcurrentMap
backing, especially for Google Guava's MapMaker, without seeing
boxing/unboxing issues moving between Java and Python code.

Fixes http://bugs.jython.org/issue2192
Unblocks http://bugs.jython.org/issue1631