gst/: Re-commit the registry changes, along with an extra fix:

gst/: Re-commit the registry changes, along with an extra fix:

Original commit message from CVS:
* gst/gst.c: (init_pre), (scan_and_update_registry),
(ensure_current_registry_nonforking),
(ensure_current_registry_forking), (ensure_current_registry),
(init_post), (gst_debug_help), (gst_deinit):
* gst/gst_private.h:
* gst/gstregistry.c: (gst_registry_finalize),
(gst_registry_remove_features_for_plugin_unlocked),
(gst_registry_remove_plugin), (gst_registry_scan_path_level),
(gst_registry_scan_path),
(_priv_gst_registry_remove_cache_plugins),
(_priv_gst_registry_cleanup):
* gst/gstregistry.h:
Re-commit the registry changes, along with an extra fix:
When a cached plugin is encountered at a different file path,
update the stored path in the registry cache so that the parent
process knows where it actually is now when it re-reads the registry
cache. Fixes the thing that broke distcheck with the previous commit.
* tests/check/Makefile.am:
Clean up files named 'core' too when running make clean.
* tests/examples/manual/Makefile.am:
Set up a registry path for running these tests, and clean it properly
for distcheck.