INT 21 P - Phar Lap 386/DOS-Extender v3.0+ - INSTALL MOD. SEG FAILURE HANDLER   
	AX = 253Ah
	ES:EBX -> function to be called when INT 21/AH=4Ah is about to return
		an error
Return: CF clear
	ES:EBX -> previous handler
SeeAlso: AH=4Ah