INT 21 - Phar Lap 386/DOS-Extender - CALL REAL-MODE PROCEDURE, REGISTERS

	AX = 2510h
	EBX = CS:IP of real-mode procedure to call
	ECX = number of two-byte words to copy to protected-mode stack to
	      real-mode stack
	DS:EDX -> pointer to parameter block (see #01360)
Return: CF clear if successful
	    all segment registers unchanged,
	    EDX unchanged
	    all other general registers contain values set by real-mode proc
	    all other flags are set as they were left by real-mode procedure
	    real-mode register values are returned in the parameter block
	CF set on error
	    EAX = error code
		01h not enough real-mode stack space
Note:	unlike most of the preceding 25xxh functions, this one is not
	  supported by FlashTek X-32VM
SeeAlso: AX=250Eh,AX=250Fh