Futures

=====

- Fixed inability to forcibly terminate the process if there are pending workers

=====

- Fixed AttributeErrors on exit on Python 2.x

=====

- Made multiprocessing optional again on implementations other than just Jython

=====

- Made Executor.map() non-greedy

=====

- Dropped Python 2.5 and 3.1 support
- Removed the deprecated "futures" top level package
- Applied patch for issue 11777 (Executor.map does not submit futures until
iter.next() is called)
- Applied patch for issue 15015 (accessing a non-existing attribute)
- Applied patch for issue 16284 (memory leak)
- Applied patch for issue 20367 (behavior of concurrent.futures.as_completed()
for duplicate arguments)

=====

- Added the set_exception_info() and exception_info() methods to Future
to enable extraction of tracebacks on Python 2.x
- Added support for Future.set_exception_info() to ThreadPoolExecutor