Log Message:
Updated fftwf to 3.3.6pl1.

FFTW 3.3.6-pl1:

* Bugfix: FFTW 3.3.6 had the wrong libtool version number, and generated
  shared libraries of the form libfftw3.so.2.6.6 instead of
  libfftw3.so.3.*.

FFTW 3.3.6:

* The fftw_make_planner_thread_safe() API introduced in 3.3.5 didn't
  work, and this 3.3.6 fixes it.  Sorry about that.
* compilation fixes for IBM XLC
* compilation fixes for threads on Windows
* fix SIMD autodetection on amd64 when (_MSC_VER > 1500)