Fix mantis 3048 (From MageKing17)

Fix "more" & offsets in [cmd|de|]briefings

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10758 387891d4-d844-0410-90c0-e4c51a9137d3
Catch a lua error that apparently can happen

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10759 387891d4-d844-0410-90c0-e4c51a9137d3
Fix a few gcc compile errors introduced by r10756

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10760 387891d4-d844-0410-90c0-e4c51a9137d3