INT 2F U - DR DOS 6.0+ FDOS EXTENSIONS - INSTALL FDOS HOOK (SHARE / DELWATCH)
	AX = 1001h
	DX:BX -> new FDOS stub entry function
Return: nothing
Notes:	the default handler for the pointer set by this call under DELWATCH
	  simply returns with CF set
	In Digital Research terminology FDOS is the part of the BDOS kernel
	  (IBMDOS.COM) responsible for the file system and related tasks, and
	  its functionality is also used by the BDOS kernel itself. However,
	  for reasons of performance and code size, it uses direct calling.
	This interrupt allows external components like SHARE file locking or
	  DELWATCH delete tracking software to hook into the internal backdoor
	  INT 2F/AH=10h/AL<=09h chain in the kernel, so that they can actually
	  allows the kernel to ensure that several conditions are met when
	  passing control to these registered components including proper
	  maintaining A20(Address line 20) The 80286 and higher CPUs allow addresses in real mode to extend slightly beyond the one megabyte mark, which causes an incompatibility with some older programs which expect such addresses to wrap back to the beginning of the address space.  For complete compatibility with the 8088, newer machines thus contain circuitry which permits the twenty-first address line (A20) to be disabled.  The CPU then effectively has only twenty address lines in real mode, just as the 8088 does, and addresses which would extend beyond the one megabyte mark wrap to the beginning of the address space.  See also High Memory Area, Real Mode., re-enterancy, or critical section mutexing
	  (e.g. getting the disk sub-system queue "MXdisk").
	The default handler in the BDOS just sets the carry flag and returns.
	Currently known clients to this shared interface are DR DOS 6.0
	  SHARE 1.xx, DR DOS 6.0+ DELWATCH 1.00+, which both chain onto
	  the same call far address, and the version of AddStor's SuperStor
	  which is bundled with DR DOS 6.0
	However, the DR PalmDOS, and Novell DOS 7 - DR-DOS 7.03 SHARE 2.00-2.05
	  do not use this function to hook into the system. Instead they fix up
	  the share stubs directly. DR PalmDOS SHARE 2.00 uses the stubs at
	  Table !!! INT 21/AH=52h, while Novell DOS 7 - DR-DOS 7.03
	  SHARE 2.01-2.05 use the private set of share stubs at Table !!! at
	  INT 21/AX=4458h).  Future releases may possibly again fix up the
	  share stubs at INT 21/AH=52h.
SeeAlso: AX=1000h,AX=F800h