Intel fftw mpi update for MKL >= 11.1

`libfftw3x_cdft_lp64.a` is now also a hard requirement when using imkl v11.1.x, which it wasn't before; this PR fixes that bug

This means that existing installations of imkl v11.1.x will have to be redone, otherwise an error message like `Not all FFTW interface libraries ['fftw3x_cdft_lp64', ...] are found in .../mkl/lib/intel64, can't set FFT_LIB.` will appear...

@hajgato, @gjbex: this basically means that the `imkl` component of `intel/2014b` will have to be reinstalled in order to use `intel/2014b` with the next EasyBuild release...