[Cython] Scope of Py_buffer

[Dag Sverre Seljebotn]

I'm wondering if I could move Py_buffer out of the default scope, in 
order to reduce the namespace incompatability. (Py_buffer is present in 
the global scope for the purposes of the second argument to 
__getbuffer__ and __releasebuffer__ ). The alternatives I see are either 
"cython.Py_buffer" or "python_buffer.Py_buffer" (or both), where you 
need to cimport cython/python_buffer first.

This means that one needs to cimport something in order to successfully 
implement __getbuffer__, however I consider this ok myself. But I 
certainly see that one could argue for it being a builtin for that reason.

As the buffer support until now has only been available for Py3/Py2.6 
which are still not released, this shouldn't need an deprecation warning 
or similar, while later it will be difficult to do this.

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Dag Sverre