NO-JIRA: Changes to python related build processes:
- Use an intermediate build area in the build area not in the source.
-- With this change the source tree is now completely untouched during
   a build.
- Fiddle with CMake so that the python install into the build area doesn't
  happen on every build.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1560851 13f79535-47bb-0310-9956-ffa450edef68