made pn_data_t an object

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1486141 13f79535-47bb-0310-9956-ffa450edef68
pn_list_index and pn_list_remove headers

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1486142 13f79535-47bb-0310-9956-ffa450edef68