Add a script to check the dist tarball, and use it to fix the dist tarball
    
    * Add a script make-dist-tarball.py that runs 'setup.py sdist' and compares
      what gets distributed with git and with a set of patterns of extra files
      added during distribution, and with git files that we don't want to
      distribute.
    
    * Extend MANIFEST.in or add __init__.py files to distribute:
    
       run-unittests.sh
       tox.in
       conf/client_secrets.json
       tests/test_builder
       tests/integration
    
    * Don't include all of module_build_service - this is too prone to backup
      files and development trash files; instead add just the files we need
      that aren't *.py
    
    * Move global-excludes to the end - they modify the existing list of files;
      and add *.db - for some reason, .mbs_local_build.db files were
      getting disted.