INT 2F - PC-DOS Econet v1.05 - INSTALLATION CHECK                               
	AX = C500h
Return: AL = status
	    00h not installed, OK to install
	    01h not installed, can't install
	    FFh installed
Note:	the interrupt-enable state will be preserved, but interrupts may be
	  enabled during processing of this function
SeeAlso: AX=C501h,AX=C508h