In response to pagmo issue #44
By default the GIL is not managed which means that multiple threads can access the Python interpreter without acquiring a lock. This default behaviour saves the hassle of the user to work with the GIL. This works perfectly fine as long as only one thread is accessing the Python interpreter, as in the case with most algorithms. However if an algorithm that spawns multiple threads (e.g. PaDe) that try to access the interpreter (because the problem is in Python) at the same time this will eventually cause segfaults.