PROTON-263: JNIDelivery.isPartial should delegate to pn_delivery_partial

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1453848 13f79535-47bb-0310-9956-ffa450edef68
PROTON-264: Have Proton-JNI hide difference in use of return values returned by methods input() and output()

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1453849 13f79535-47bb-0310-9956-ffa450edef68
PROTON-266: Fix JNIMessage#setBody to actually set the _body member

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1453850 13f79535-47bb-0310-9956-ffa450edef68