opal_free_list_item_t and everyone was just treating them as
opal_list_itme_t structures, which meant that they were overwriting the
user_data memory anyway. So make an opal_free_lsit_item_t be just a
opal_list_item_t.
Also, opal_free_list_item_t wasn't a proper class, which made it slightly
less than nice to use, so fix that part up. Also update the
opal_free_list_t to use the class macros, so that it is more obvious we
actually do the right thing.
This commit was SVN r10304.