put back source in registry. add checks for find_plugin.

put back source in registry.  add checks for find_plugin.

Original commit message from CVS:

* check/gst/.cvsignore:
* check/gst/gstplugin.c: (GST_START_TEST), (gst_plugin_suite):
* gst/gstregistryxml.c: (load_plugin),
(gst_registry_xml_save_plugin):
put back source in registry.  add checks for find_plugin.
* testsuite/states/bin.c: (assert_state), (empty_bin),
(test_adding_one_element), (main):
* testsuite/states/locked.c: (main):
some compile/run fixes