INT 21 - U - PTS-DOS 6.51 & S/DOS 1.0 - EXTENDED RENAME FILE USING FCB

	AH = 18h
	DS:DX -> modified FCB (see also #01345)
Return: AL = status
	     00h successfully renamed
	     FFh no matching files,file is read-only, or new name already exists
Notes:	This function is provided by Paragon Technology Systems S/DOS 1.0
	  (and most probably also PTS-DOS 6.51, maybe even earlier). It uses
	  the same code as for function INT 21/AH=17h, but additionally sets
	  an internal "SERVER" flag on entry. Apparently this results in
	  different usage of attributes and wildcards.
	It is currently unknown if this function is also supported by
	  PhysTechSoft's PTS-DOS 6.60, 6.70, or 2000.
SeeAlso: AH=17h,AH=0Fh,AH=13h,AX=4303h,AH=56h,INT 2F/AX=1111h,INT21/AH=5Dh