Fix a problem when using -fork with an MPI-enabled build. We initialize MPI
before even parsing options, so if/when we are to fork later on, we need to
tear that "1-node MPI session" down before forking, or the forked MPI world
will result in all sorts of funny business. Tricky stuff.
Wordlist.c bugfix: Do not try to split-load a too small file into buffer.