Fix issue #494 (some log info was printed once per forked process)

Since this is a core bug, the core version should be changed
in a similar way.
fix typo in comment
Re-add an "if (john_main_process)" that is needed for MPI
Merge pull request #553 from frank-dittrich/bleeding-jumbo

Fix issue #494 (some log info was printed once per forked process)