Fix purepython builtin type strings

Speed up cpdef method override checks also for Python subclasses with slots by assuming that slot attributes themselves never override type fields in the parent class (Python raises an error if you try).
See #2313.

This does not help for classes with "__slots__", nor does it help for alternating calls to different objects.
There is probably still space for improvements, e.g. by using an array of object dict versions.
See #2313.

Using __new__ was made an error 8 years ago, keeping this in the docs just causes confusion at this point (e.g. #2311).

Make raise-statements inside of nogil blocks automatically acquire the GIL, instead of requiring an explicit ``with gil`` block around them.

Fix: reallowing tp_clear() in a subtype of an @no_gc_clear extension type generated an invalid C function call to the (non-existent) base type implementation.
Closes #2309.

Add decrlarations from ceval.h

Add PyEval_InitThreads and PyEval_ThreadsInitialized

Added an example of iteration for x in vector.

Closes #1771.

This reverts commit eb0e4666.

Fix importing of namespace packages. Add in a regtest for the same.

Fix warning about "comparison between signed and unsigned" in example and make it fully C89 compatible.

Updated runtests to exclude the pyximport_namespace test. Implicit namespace packages were introduced in Python 3.3.

Added tests for the convolve with the memoryviews in the docs.

Remove redundant helper function "__Pyx_ImportModule()" which was only needed in Py<2.6 when PyObject_GetAttrString() and PyImport_ImportModule() did not take const string arguments.

Mark several one-time functions (used during module init) with CYTHON_SMALL_CODE to reduce their binary code impact on the overall module size.