Cython is still built and installed with the standard distutils
setup.py mechanisms, but this allows other bazel projects to
reference and use Cython as part of their build process.

try to work around a Py_FatalError crash in latest Py3.6 apparently due to a RuntimeWarning during garbage collection

Replace old build_ext with new cythonize(...) version.

This closes #1433.

p_f_string_expr produced warning: implicit conversion loses integer precision: 'long' to 'Py_UCS4' (aka 'unsigned int') [-Wshorten-64-to-32]

Closes #1458.

Support dependencies in conditional compilation

Adds support for simple FakeReference equality testing.

setup.py shouldn't write arbitrarily to stdout (especially when passed display options)

The old build_ext is now named old_build_ext, replaced with the one from Cython/Build.

In general it's best for actions performed in `setup.py` to be deferred until the command to which they are relevant is actually run.  For example most of what `compile_cython_modules` does should be deferred until finalizing the `build_ext` command.  But as a simpler workaround, just ensure that anything it prints is to stderr.

Otherwise this breaks certain assumptions, such as that `./setup.py --name` will print (on stdout) the distribution name (and nothing else), and likewise for `./setup.py --version`.

Cython.Build brings in cythonize, which is not in a Py3.2 compatible file.

Fix overriding of cdef by cpdef method in .pxd file