Some changes to the grenade launcher and shotgun that weren't my changes

Some changes to the grenade launcher and shotgun that weren't my changes
SUB_Null changed to nullfunction
More deathtypes added for falling, falling down endless pits, drowning, and trigger_hurt
trigger_hurts can have custom death messages (set .message field to something like "was in the wrong place." Make sure there is no space at the beginning and it ends with a punctuation character.)

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@251 f962a42d-fe04-0410-a3ab-8c8b0445ebaa