INT 21 - European MS-DOS 4.0 - "SETPRI" - GET/SET PROCESS PRIORITY
	AX = 8E00h
	BH = 00h
	BL = action
	    00h set priority for command subtree
	    01h set priority for specified process only
	CX = Process ID
	DH = 00h
	DL = change in priority (00h to get priority)
Return: CF clear if successful
	    DL = process priority
	    DH destroyed
	CF set on error
	    AX = error code (01h,no such process)(see #01680 at AH=59h)
Desc:	specify or determine the execution priority of the specified process
	  or the process and all of its children
SeeAlso: AH=81h