INT 21 P - Phar Lap 386/DOS-Extender VMM - EXHANGE TWO PAGE-TABLE ENTRIES       
	AX = 251Fh
	BL = address type
	    00h linear address
		ECX = linear address of first page table entry
		EDX = linear address of second page table entry
	    01h pointer
		ES:ECX -> first page table entry
		ES:EDX -> second page table entry
Return: CF clear if successful
	CF set on error
	    EAX = error code
		09h invalid address or NOPAGE option set
		82h not compatible with DPMIsee DOS Protected-Mode Interface
SeeAlso: AX=251Dh,AX=251Eh