PROTON-552: Centralise defintions of bool/true/false and make it work as C
on Visual Studio too

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1584732 13f79535-47bb-0310-9956-ffa450edef68
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.

git-svn-id: https://svn.apache.org/repos/asf/qpid/proton/trunk@1584733 13f79535-47bb-0310-9956-ffa450edef68