Switch from using H5L_index_t/H5L_INDEX_<foo> to H5_index_t/H5_INDEX_<foo>
in order to accommodate indices on aspects of attributes as well as links.
Add basic support for deleting attributes in dense storage (needs more
support/tests for shared attributes in dense storage still).
Misc. cleanups, etc.
Tested on:
Linux/32 2.6 (chicago)
Linux/64 2.6 (chicago2)