Original commit message from CVS:
merge in tagging
Includes:
- gsttag.[ch] - The definition of GstTagList and tag registering/querying
- gsttaginterface.[ch] - Interface for elements that can handle setting of tags
- updates and merges to gststructure.[ch] and gstvalue.[ch]
- testsuite/tags - some tests for tagging
- bugfixes
- updates to make make distcheck work
- updates the version number to 0.7.2.1

Does not include:
- including tagging stuff in docs
- extensive tests