This patch comes from Ben Reser. It makes our typedefs consistently use a
structure tag with the same name as the typedef. Providing a structure tag for
each structure can help when using gdb.
(There is also a more minimal version of this patch which just fixes the one
instance of a mismatched structure tag, which screws up doxygen. But I'm
proposing the less minimal patch since it's zero-risk and it cleans up the API a
bit. See http://www.contactor.se/~dast/svn/archive-2004-01/0025.shtml for the
more minimal patch.)