Multiple improvements.

Fixes the security exception by calling jython in a forked process. No JVM policy changes needed any more.
Bootstraps a full version of Jython.
Installs setuptools, pyyaml, and ccm.
ant only rebuilds things if it needs to (ie, build directory is missing)

Setuptools is somewhat broken in that it cannot download packages due to a bug in Jython 2.7: http://bugs.jython.org/issue2066
For now, packages are installed via tarball from the pylib/ directory.