Add Further Support for Google App Engine

Upgraded `django-pipeline` to `1.3.10`, and started getting a rather unpleasant looking error: `"ImportError: cannot import name _args_from_interpreter_flags"`.

As highlighted in Issue #231, the root of this problem lies in the use of the Python package, `multiprocessing` ... I'm working with `django==1.5` via GAE SDK `1.8.8`. 

As highlighted in Issue #231, GAE does not support `multiprocessing`. However, there is [now] a `concurrent` package in the SDK folder, `google_appengine/lib/concurrent`.

Although a fix is discussed in Issue #231 it somehow seems to have disappeared in the code base.

If this commit is acceptable I can update the docs accordingly. If this commit is unacceptable please do make a suggestion on how we can better include a skip on the concurrent components of code.

Raj.