[Numpy-discussion] [REVIEW] Update NumPy API format to support updates that don't break binary compatibility

[Stéfan van der Walt]

The current NumPy API number, stored as NPY_VERSION in the header files, needs
to be incremented every time the NumPy C-API changes.  The counter tells
developers with exactly which revision of the API they are dealing.  NumPy does
some checking to make sure that it does not run against an old version of the
API.  Currently, we have no way of distinguishing between changes that break
binary compatibility and those that don't.

The proposed fix breaks the version number up into two counters -- one that gets
increased when binary compatibility is broken, and another when the API is
changed without breaking compatibility.

Backward compatibility with packages such as Matplotlib is maintained by
renaming NPY_VERSION to NPY_BINARY_VERSION.

Please review the proposed change at http://codereview.appspot.com/2946

Regards
Stéfan