DMG formats: even more debugging
Always start a resumed session by emitting status.
Reload upon SIGUSR2 or --reload-every=N seconds. A reload is currently
the same as stopping a job and then resuming it, it's not very optimized.
Still, it can be invaluable eg. for forked sessions with salts.
However, the current implementation (execv) is not supported under MPI,
which is a major problem.

This patch probably also fixes some bugs in timers for --progress-every
and --max-run-time on certain systems.
DMG-opencl add missing variable from 74ac62a.
Minor bug in "reload" patch: Some output to stdout was supposed to
go to stderr.