New comments for C API.


git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1529999 13f79535-47bb-0310-9956-ffa450edef68
PROTON-440: fix from hiram

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1531508 13f79535-47bb-0310-9956-ffa450edef68