Stopgap fix to avert a crash in get_subsystem_world_pos later on


git-svn-id: svn://svn.icculus.org/fs2open/trunk@10738 387891d4-d844-0410-90c0-e4c51a9137d3
Fix mantis 2812 (From Yarn)

Add modular help tables and allow more than 2 help overlays

git-svn-id: svn://svn.icculus.org/fs2open/trunk@10739 387891d4-d844-0410-90c0-e4c51a9137d3