Fix for Mantis 2882 by Mageking17 (change-team-color with None color results in error)

git-svn-id: svn://svn.icculus.org/fs2open/trunk@10914 387891d4-d844-0410-90c0-e4c51a9137d3
From Axem: Add ba.getGameDifficulty() scripting function to get the current difficulty level.

git-svn-id: svn://svn.icculus.org/fs2open/trunk@10916 387891d4-d844-0410-90c0-e4c51a9137d3