PROTON-535: point PYTHONPATH to build locations for epydoc invocation; hopefully this should prevent local installs from interfering with source builds

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1584359 13f79535-47bb-0310-9956-ffa450edef68
doxygen for message.h

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1584367 13f79535-47bb-0310-9956-ffa450edef68
PROTON-552: Centralise defintions of bool/true/false and make it work as C
on Visual Studio too
PROTON-552: Change code to be C89 compatible

The Visual Studio C compiler before VS2013 only supports variable
declarations at the start of a code block. So change any files that are
compiled as C under Visual Studio to conform to this.