INT 2F U - DOS 3.0+ internal - SIGNAL SHARING VIOLATION TO USER                 
	AX = 120Bh
	ES:DI -> system file table entry for previous open of file
	STACK: WORD extended error code (should be 20h--sharing violation)
Return: CF clear if operation should be retried
	CF set if operation should not be retried
	    AX = error code (20h) (see #01680 at INT 21/AH=59h/BX=0000h)
	STACK unchanged
Notes:	can only be called during a DOS function call
	should only be called if an attempt was made to open an already-open
	  file contrary to the sharing rules
	invokes INT 24 if SFTsee System File Table file opened via FCBsee File Control Block or in compatibility mode with
	  inheritance allowed