cInventory: Added the ChangeSlotCount() function to the Lua API

git-svn-id: http://mc-server.googlecode.com/svn/trunk@1683 0a769ca7-a7f5-676a-18bf-c427514a06d6
cItemGrid: ChangeSlotCount() now returns -1 if invalid SlotNum

git-svn-id: http://mc-server.googlecode.com/svn/trunk@1684 0a769ca7-a7f5-676a-18bf-c427514a06d6