Reinstall fftw into MPI category

- Minor Updates based on Achim's suggestions.

MPI/fftw/README

@@ -0,0 +1,7 @@
+FFTW
+====
+
+FFTW is highly optimized, but downgrades if run on an older processor. It
+should be built compiled on a system with SSE2 and AVX2 support (e.g. merlin).
+
+This module requires PMODULE_VERSION > 1.0.0 to compile.

MPI/fftw/build

@@ -1,6 +1,7 @@
 #!/usr/bin/env modbuild
+# Needs to be built with SSE2 and AVX2 support, but should run on architectures without this
 
-pbuild::add_to_group 'Compiler'
+pbuild::add_to_group 'MPI'
 
 pbuild::set_download_url "http://www.fftw.org/fftw-$V.tar.gz"
 pbuild::set_sha256sum "fftw-3.3.8.tar.gz:6113262f6e92c5bd474f2875fa1b01054c4ad5040f6b0da7c03c98821d9ae303"

MPI/fftw/files/variants

@@ -1,2 +1 @@
-fftw/3.3.8	unstable	gcc/8.2.0 mpich/3.2.1 openmpi/3.1.3
-fftw/3.3.8	unstable	gcc/7.3.0 mpich/3.2.1 openmpi/3.1.3
+fftw/3.3.8	unstable	gcc/{7.3.0,8.2.0} mpich/3.2.1 openmpi/3.1.3

MPI/fftw/modulefile

@@ -6,7 +6,10 @@ module-license      "GPL; http://www.fftw.org/doc/License-and-Copyright.html"
 module-maintainer   "Spencer Bliven <spencer.bliven@psi.ch>"
 
 module-help         "
-FFTW is a C subroutine library for computing the discrete Fourier transform (DFT) in one or more dimensions, of arbitrary input size, and of both real and complex data (as well as of even/odd data, i.e. the discrete cosine/sine transforms or DCT/DST).
+FFTW is a C subroutine library for computing the discrete Fourier transform
+(DFT) in one or more dimensions, of arbitrary input size, and of both real and
+complex data (as well as of even/odd data, i.e. the discrete cosine/sine
+transforms or DCT/DST).
 "