INT 21 u - European MS-DOS 4.0 - "PBLOCK" - BLOCK A PROCESS
	AH = 99h
	DS:BX -> memory location to block on
	CX = timeout in milliseconds
	DH = nonzero if interruptable
Return: CF clear if awakened by event
	    AX = 0000h
	CF set if unusual wakeup
	    ZF set if timeout, clear if interrupted by signal
	    AX = nonzero
Desc:	suspend calling process until another process sends a "restart" signal
	  or a timeout occurs
SeeAlso: AH=9Ah,INT 2F/AX=0802h