Add metadata reading example that loops over a list of filenames, dumping any tags...

Add metadata reading example that loops over a list of filenames, dumping any tags found.

Original commit message from CVS:
* configure.ac:
* examples/Makefile.am:
* examples/metadata/Makefile.am:
* examples/metadata/read-metadata.c: (message_loop),
(have_pad_handler), (make_pipeline), (print_tag), (main):
Add metadata reading example that loops over a list of filenames,
dumping any tags found.

* gst/gstbus.c: (gst_bus_dispose):
* gst/gstelement.c: (gst_element_dispose):
Release a few potentially-held references in dispose.