INT D4 - PC-MOS/386 v5.01 - GET/SET TASK PRIORITY                               
	AH = 1Ah
	AL = subfunction (00h read, 01h set, 02h get and set)
	BX = task ID (FFFFh for current task)
	CL = new priority value
Return: CF clear if successful
	    CL = current priority value
	CF set on error
	    AX = error code (see #01680 at INT 21/AH=59h/BX=0000h)
SeeAlso: AH=1Bh,AH=1Ch