INT 2F U - 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(Terminate and Stay Resident) A program which remains in memory after terminating in order to provide services to other programs or the user.  The name comes from the name of the DOS function call used to remain in memory after termination. 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


Format of COMMAND.COM command line buffer:
Offset	Size	Description	(Table 02977)
 00h	BYTE	max length of command line, as in INT 21/AH=0Ah
 01h	BYTE	count of bytes to follow, excluding terminating 0Dh
      N BYTEs	command line text, terminated by 0Dh


Format of command name buffer:
Offset	Size	Description	(Table 02978)
 00h	BYTE	length of command name
 01h  N BYTEs	uppercased command name (blank-padded to 11 chars by 4DOS v4)