PROTON-597: update TransportOutputAdaptor and FrameParser to release buffers after use, reducing memory consumption when using large frame sizes

Change from Marcel Meulemans

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1606010 13f79535-47bb-0310-9956-ffa450edef68
PROTON-597: remove use of the scratch buffer which will always be 512bytes due to minMaxFrameSize, and instead write bytes straight to the output buffer

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1606011 13f79535-47bb-0310-9956-ffa450edef68
PROTON-597: only release transport buffers if they are above a threshold capacity

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1606012 13f79535-47bb-0310-9956-ffa450edef68