INT 21 - Phar Lap 386/DOS-Extender, Intel Code Builder - INSTALLATION CHECK     
	AH = 30h
	EAX = 00003000h
	EBX = 50484152h ("PHAR")
Return: AL = major DOS version
	AH = minor DOS version
	EAX bits 31-16 = 4458h ('DX') if 386/DOS-extender installed
	    BL = ASCII major version number
	EAX bits 31-16 = 4243h ('BC') if Intel Code Builder installed
	    EDX = address of GDA
SeeAlso: AX=2501h,AX=FF00h,INT 2F/AX=F100h