PROTON-677: added support for detach

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1627098 13f79535-47bb-0310-9956-ffa450edef68
PROTON-679: patch from dominic for manual credit mode

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1627102 13f79535-47bb-0310-9956-ffa450edef68
PROTON-680: link and delivery accessors (patch from dominic)

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1627106 13f79535-47bb-0310-9956-ffa450edef68