heads up: gufuncs on empty arrays and NpyIter removal of empty axis
just a small heads up for gufunc hackers and low level iterator users.
We will probably very soon put in a commit into master that will allow
the removal of empty axis from NpyIter/nditer, effectively removing the
"ValueError: cannot remove a zero-sized axis from an iterator"
If this creates problems for you, please tell, so that we can slow down
or undo the change. As an example, we have a matrix_multiply gufunc for
testing purpose, which did not zero out the output for the case of
`matrix_multiply(np.ones((10, 0)), np.ones((0, 10)))`. So this could
turn code that errored out for weird reasons into wrong results in rare