INT 2F - DOS 3.3+ internal - INSTALLABLE COMMAND - INSTALLATION CHECK

	AX = AE00h
	DX = magic value FFFFh
	CH = FFh
	CL = length of command line tail (4DOS v4.0)
	DS:BX -> command line buffer (see #02977)
	DS:SI -> command name buffer (see #02978)
	DI = 0000h (4DOS v4.0)
Return: AL = FFh if this command is a TSR extension to COMMAND.COM
	AL = 00h if the command should be executed as usual
Notes:	This call provides a mechanism for TSRs to install permanent
	  extensions to the command repertoire of COMMAND.COM.	It appears
	  that COMMAND.COM makes this call before executing the current
	  command line, and does not execute it itself if the return is FFh.
	APPEND hooks this call, to allow subsequent APPEND commands to
	  execute without re-running APPEND
SeeAlso: AX=AE01h