Warn in numpy/distutils/command/egg_info.py if using setuptools.sdist.

See gh-7127 for details.

The 'sys.executable' can come in various names, but
the three main ones are "python", "python{major_version}",
and "python{major_version.minor_version}". The current
version of the f2py test assumes that only the latter
two are used. Since "f2py" is generally versioned,
using the executable basename "python" will make it
impossible to find. This commit fixes that issue
by using a sure-fire way of getting the Python version.

Fixed test_scripts.test_f2py test so that
it can pass correctly on win32 virtualenvs,
in which the Python executable and the
f2py.py file are both in the Scripts
directory.

Fixes bug in np.random methods that would return scalars
when passed one-element array inputs. This is because
one-element ndarrays can be cast to integers / floats, which
is what functions like PyFloat_AsDouble do before converting
to the intended data type.

This commit changes the check used to determine whether the
inputs are purely scalar by converting all inputs to arrays
and checking if the resulting shape is an empty tuple (scalar)
or not (array).

Closes gh-4263.

Clarified the output size depending on whether
scalar or non-scalar inputs are passed to
functions in mtrand.pyx that can broadcast
their arguments.

Added a whole new suite of tests to ensure that
functions in mtrand.pyx which are broadcastable
actually broadcast their arguments properly.