INT 31 - CauseWay - "GetMemDOS" - ALLOCATE CONVENTIONAL MEMORY

	AX = FF21h
	BX = number of paragraphs to allocate
Return: CF clear if successful
	    AX = real-mode segment of allocated block
	    DX = initial selector for block
	CF set on error
	    AX = DOS error code (see #01680 at INT 21/AH=59h/BX=0000h)
	    BX = size of largest available block
Note:	if the requested size is greater than 64K, contiguous selectors will
	  be allocated, one for each 64K; for 32-bit applications, the first
	  selector's limit will be set to the size of the entire block, while
	  that selector will have a limit of 64K for 16-bit applications.  All
	  selectors after the first one have a limit of 64K except the final
	  one
SeeAlso: AX=FF22h,AX=FF23h,INT 21/AH=48h