FIX: prevent missing cimport warnings when using cythonize.

The `cython` package fakes several sub-modules, including
`cython.operator` and `cython.view`. Since the `cythonize` command
cannot find a corresponding pxd file for these modules, it prints
a warning. To fix this, we exclude all modules in the `cython`
namespace when checking for missing pxd files.

 cyfunction defaults

Change __Pyx_zeros and __Pyx_minusones scope to static.

Compiling two Cython modules (which use the Cython buffer interface)
into a static Python binary results in a link error since the symbols
`__Pyx_zeros` and `__Pyx_minusones` are exported multiple times.  Changing
their scope to the current translation unit fixes the issue.