Expose K_AddMessage functions.

New Functions.

K_AddMessage(string msg, boolean interrupt, boolean persist)

K_AddMessageForPlayer(player_t player, string msg, boolean interrupt, boolean persist)

K_ClearPersistentMessages()

K_ClearPersistentMessagesForPlayer(player_t player)

Only used in battle mode, so why not :]

k_addmessagetest.lua