Fix for bug 687: Makes JarUtil work with custom classloaders

Added the ability for users to set a "resolver" in JarUtil that lets it find resources that are loaded by a custom classloader. This is needed in OSGi apps (like Eclipse RCP apps), since OSGi resources do not have simple jar: URLs (they use a custom protocol called bundleresource:).

I've tested this fix on Windows 7 64-bit, Mac OS X 10.7.5, and Ubuntu 12 64-bit, and it works on all three. There's also a unit test included :)