Redefine uri:classloader: meaning

redefine uri:classloader: meaning to be the parent classloader of runtime.getJRubyClassLoader
    
this allows to set JRubyHome to uri:classloader:/META-INF/jruby.home for all situations where there is a jruby.home packed inside a jar.
    
fixes problem with loadService and knoplerfish OSGi and activated the tests for knoplerfish

@enebo @ratnikov I made this against the jruby-1_7 and hope this OK since it is only used by IsolatedScriptingContainer and has no effect on the rest of JRuby. 
@kares if jruby-rack would accommodate the IsolatedScriptingContainer via some config or so, then this could finally fix websphere or jboss-wildfly packed with warbler (not sure what surprises bundler has).