Dummy versions of FFTW's fftw_init_thread() and fftw_cleanup_thread functions.

These are only compiled if pyNFFT is built against a non-threaded version of
FFTW; the information is passed from setup.py to the C compiler via a
config.h file created by setup.py in pynfft.
Support combined (single- and multi-threaded) fftw3 library on Windows.
Added (quick & dirty) command line options to setup.py.