Update OSGi classloader

I've added an OSGi integration test.  Currently it needs to be run after ant jar-jruby-complete and you need to use either the felix2 or felix4 profile.  I'm open to suggestions for how to better integrate the test case.

After adding the test case, I added a different method to find the classloader for a bundle.  I added this as a set of new classes, mostly because I wanted to ensure any users of the existing classes wouldn't be affected.

I verified that the new method does fallback correctly in the felix2 profile (which doesn't export the new org.osgi.framework.wiring package.