INT 21 - VIRUS - "Tremor" - INSTALLATION CHECK
	AX = F1E9h
Return: AX = installation state
	    CADEh installed, and calling program is infected
	    F100h not installed (normal DOS return value)
	    else  installed, but calling program is not infected
SeeAlso: AH=F1h"VIRUS",AX=F2AAh