INT 21 - Phar Lap 386/DOS-Extender - ALLOCATE MS-DOS MEMORY BLOCK

	AX = 25C0h
	BX = number of 16-byte paragraphs of MS-DOS memory requested
Return: CF clear if successful
	    AX = real-mode paragraph address of memory
	CF set on error
	    AX = error code
		07h MS-DOS memory control blocks destroyed
		08h insufficient memory
	    BX = size in paragraphs of largest available memory block
SeeAlso: AX=25C1h,AX=25C2h