BUG: initialize op_axes when only itershape is given

In this case, the initialization used the number of dimensions instead
of setting it to NULL for each operand, leading to possible segmentation
faults.
2to3: Put `from __future__ import division in every python file.

This should be harmless, as we already are division clean. However,
placement of this import takes some care. In the future a script
can be used to append new features without worry, at least until
such time as it exceeds a single line. Having that ability will
make it easier to deal with absolute imports and printing updates.
MAINT: Make numpy/f2py/crackfortran docstring read better.

The copyright and short summary were moved to the top of the
docstring with the usage description below.
Merge pull request #3102 from seberg/nditer-fix-op_axes-initialization

BUG: initialize op_axes when only itershape is given
Merge pull request #3026 from charris/2to3-fix-print

2to3: Put `from __future__ import division` in every python file.