Get jruby-jars to build correctly

The core of this PR is a fix in JarResource to use jarEntry rather that (entry)path as the name of the jar file. Oops.

The rest of the PR provides some minor enhancements and explicitness of behavior:

1) If you require foo_test.jar!/foo.rb it still loads the foo.rb entry of the foo_test.jar, but now $LOADED_FEATURES will still denote foo_test.jar!/foo.rb
2) Extracted the logic when LibrarySearcher bypasses LOAD_PATH, since it's somewhat complicated when dealing with schema.