tracing/pyruntraced: New tool to run Python code with tracepoints activated (draft)

We will hopefully need it in the future to test external python code
similarly to when testing in-process go code with the help of
tracepoints. See module description for details (tracetest is not yet
done).

There is no yet Go client API for interacting with such-traced python
program. For the record: manually inspecting traced python process could
be done via e.g.

	socat EXEC:"./pyruntraced 3 neo.trace.py -- ../../../t/backup-play/N1-writer",fdin=3,fdout=3 TCP:localhost:8888

and telnetting to localhost:8888 from another xterm.