This code branches out of the alpha/early_adopter code and begins
building toward the beta API.

Use it to validate that arithmetic on time types makes even some vague
kind of sense.

Conflicts:
	src/python/src/setup.py

Conditionally runs the tests depending on the availability of Python
versions (because Travis is the worst).

Also set up environment-related details needed for a smooth Cython
experience: have the test script avoid rebuilding all dependencies if the
virtualenv directory already exists, have the PyPI distribution script
distribute the Cython generated C code rather than the .pyx files.

Pull request #1577 removes the backup poller internal to completion
queues so this test needs to use extra threads to drive the work done
inside the completion queues by continuously calling each completion
queue's get method.

The previous timeout was short enough that it led to erroneous failures.

Fixes #1875.

Introduced grpc_byte_buffer_init instead. It's now the user's responsibility to
manage memory.

Exposes the C core batch API to the Python layers. Provides a shim to
enable the old Python API to remain the same (for now).

Fixes #1762.

Updated to version 0.9.0a0.

Fixes #1591.

Also fixes a raised-exceptions-during-tests-causes-hanging problem.

This defect was originally introduced in Google-internal source control
on 18 August 2014. Wow. Clearly unit test coverage is needed for this
feature.