There may be a way to use third_party's protobuf (and this
may eventually be necessary) but I haven't yet figured out
how to do it correctly. It can happen later.

The source code is moved from src/python to
src/python/src. A setup.py is added at
src/python. The build_python.sh and
run_python.sh scripts are updated to build
and run the Python tests by building a
package and installing it in the developer's
Python 2.7 virtual environment.