Messages
There are a maximum of 63 message types, so a bitmask can be passed.  Messages 
have two args.  See Message Codes.

FlushMsgs           Funct Throw away all messages. Return count.
GetMsg              Funct Wait for a message of type specified by a one in the mask.
Msg                 Funct Post message to current task and return immediately.
PostMsg             Funct Post message to a task and return immediately. See msg_code.
PostMsgWait         Funct Post message to a task and wait until task is idle.See msg_code.
ScanMsg             Funct Check for a message of type specified by a one in the mask.
TaskMsg             Funct Post message to servant task. Tell who the master task is.
sys_focus_task      GlbVar Current focus task.