INT 15 - Rational Systems DOS/16M - INSTALLATION CHECK                          
	AX = BF02h
	DX = 0000h
Return: DX = nonzero if installed
	    DX:SI -> XBRK structure (see #00508)
Note:	this function is also supported by DOS/4G
SeeAlso: AX=BF01h,AX=BFDCh,AX=BFDEh/BX=0000h
SeeAlso: INT 21/AH=FFh/DH=0Eh,INT 2F/AH=A1h,INT 2F/AX=F100h,INT 2F/AX=FBA1h


Format of DOS/16M XBRK structure:
Offset	Size	Description	(Table 00508)
 00h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	linear address of first available byte
 04h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	linear address of last available byte + 1 ???
 08h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	real-mode address of XBRK structure???
 0Ch	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	???
 10h  2 BYTEs	???
 12h	WORD	segment of ???
 14h  8 BYTEs	???
 1Ch 512 BYTEs	protected-mode IDTsee Interrupt Descriptor Table
21Ch  N BYTEs	protected-mode GDT