MPI vs. fork fixes, and documentation.
Fix GPU builds after recent core merges.
MPI: Drop obsoleted output.
Revert "SIP valid() fix."

This reverts commit c5933c8b64c4515172a6a192166a41fa80e7c864.
MPI: If OMP_NUM_THREADS is set, we assume the user knows what he is doing.
Here's how to pass it to remote hosts:
 mpirun -x OMP_NUM_THREADS=4 -np 2 -host ...
Tune a couple of "FIXME" OMP_SCALE macros.
Add lanman.chr made from Rockyou (repaired and converted to CP858 - superset
of CP437 - and split at length 7).
Merge remote-tracking branch 'upstream/bleeding-jumbo' into paths-rework