fix refcounting tests so that they compile and run, but they fail currently: gst leaks obscene amounts of memory ;) f...

Original commit message from CVS:
* fix refcounting tests so that they compile and run, but they fail currently:
gst leaks obscene amounts of memory ;)
* fix plugin loading test so that it only refers to plugins within the gstreamer/
tree
* store gst plugin paths in the registry
* is GST_REGISTRY is set, only use the user registry with the PLUGIN_PATH explictly
specified by the user
* all tests should pass now except refcounting