Move gem generation probability overrides to mkobj.

And don't hardcode the total probability of gems.
Remove a hardcoded constant from makedefs.
Merge remote-tracking branch 'dtsund/savebreak' into savebreak
Why on earth would you render a message but not mark it as seen.

Fixes #402.
Do a bit more checking of temporary object IDs.
Clean up a bit of global state in level changes.

This fixes a heinous display bug when you died between levels.
Stop using (0, 0) as a dummy location for migration.
More column indexing fixes.
Merge remote-tracking branch 'coppro/savebreak' into savebreak

Conflicts:
	libnethack/src/end.c
	libnethack/src/pager.c
Merge remote-tracking branch 'dtsund/savebreak' into savebreak

Conflicts:
	nethack/src/messages.c