PROTON-581: part2, pick up minor changes since review board version

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1627987 13f79535-47bb-0310-9956-ffa450edef68
PROTON-668: Document Proton-c IO restrictions for 0.8 release

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1627988 13f79535-47bb-0310-9956-ffa450edef68