split transport code out of engine.c

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1518183 13f79535-47bb-0310-9956-ffa450edef68
added initializer; switched definitions over to using PN_CLASS macro

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1518264 13f79535-47bb-0310-9956-ffa450edef68
implemented route and rewrite for java Messenger

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1518740 13f79535-47bb-0310-9956-ffa450edef68