Use of PME requires FFTW support, but licensing prevents its distribution
with MDX.  Instructions for building FFTW support into MDX:
   - download FFTW version 2.1.5:
      + http://www.fftw.org/fftw-2.1.5.tar.gz
      + ftp://ftp.fftw.org/pub/fftw/fftw-2.1.5.tar.gz
   - copy files from the fftw and rfftw directories into respective
     MDX directories, e.g.:
      + cp fftw-2.1.5/fftw/* mdx/src/fftw
      + cp fftw-2.1.5/rfftw/* mdx/src/rfftw
   - reconfigure MDX for FFTW support and rebuild, e.g.:
      + cd mdx
      + make config HAVE_FFTW=yes
      + make clean
      + make
      + make install