[SI:DTP-INDEXED-FORWARD][CDR-CODE][ADDRESS]

Should act like an invisible pointer into SI:*INDEXED-CELL-ARRAY* 
which will be an ART-Q array. Like DTP-ONE-Q-FORWARD but with an index.

If DTP-INDEXED-FORWARD is seen then the machine will get the word
 (AREF SI:*INDEXED-CELL-ARRAY* ADDRESS)

If SI:*INDEXED-CELL-ARRAY* is not an array or not big enough then we should probably
signal a trap much like a DTP-TRAP error. 

A suggestion: to return NIL since programs like the inspector will not expect to
find cells like SYMBOL-PLIST unbound. What about PUTPROP in this case?
Clearly it should be an error. 

Or ADDRESS is actually [SEMANTICS][INDEX]
where [SEMANTICS] controls default behavior. e.g. 0 = unbound/trap, 1 = NIL.


Programs to worry about:
 * inspector, must have SYMBOL-PLIST-BOUNDP.
 * error handler. must have binding of SI:*INDEXED-CELL-ARRAY* from stack group being
   debugged.
 * special closures. Exactly what cell is going to be recorded as the internal value cell?
 * property lists, e.g.

 XCL1
        (call-data-type-not-equal pdl-top (a-constant (byte-value q-data-type dtp-symbol)) trap)
   (ERROR-TABLE ARGTYP SYMBOL PP T)
   (ERROR-TABLE ARG-POPPED 0 PP)
	(POPJ-AFTER-NEXT 
	 (M-T) DPB Q-POINTER PDL-POP 
		(A-CONSTANT (BYTE-VALUE Q-DATA-TYPE DTP-LOCATIVE)))
       ((M-T) ADD M-T A-TEM1)


 Code from rplacd:
			   (LOCF (SYMBOL-PLIST SYMBOL-OR-PLIST))
			 SYMBOL-OR-PLIST))
	   (RPLACD PLLOC (LIST*-IN-AREA (IF (= (%AREA-NUMBER SYMBOL-OR-PLIST) NR-SYM)

This gets the locative 			   (LOCF (SYMBOL-PLIST SYMBOL-OR-PLIST))
 using XCL1 index (TEM1) = 3. But RPLACD should do
the right thing here.


Higher level constructs:

Given a symbol, allocate slots in SI:*INDEXED-CELL-ARRAY* for its value, function, and property lists.
Then copy the contents of those cells into the array. Then store DTP-INDEXED-FORWARD's into the
symbol.



 microcode dispatch tables effected.
 * many tables have INDEXED-FORWARD handled like what small float (which type used to be)
   used to do. FIX THESE.

Trans-*

	(INHIBIT-XCT-NEXT-BIT TRANS-OLD0)	;0 ONE-Q-FORWARD
	(INHIBIT-XCT-NEXT-BIT TRANS-OQF)	;1 ONE-Q-FORWARD
 
	(INHIBIT-XCT-NEXT-BIT PB-TRANS)		;0 ONE-Q-FORWARD
	(P-BIT R-BIT)				;1 ONE-Q-FORWARD

D-GC-WRITE-TEST
	(n-bit gc-write-trap)			;0 ONE-Q-FORWARD
	(R-BIT)					;1 ONE-Q-FORWARD


CALL-INSTANCE-KEY-FOUND
    .....
	((VMA-START-READ) ADD M-B (A-CONSTANT 1))  ;Assumes no ONE-Q-FORWARDs in the hash table.
	(CHECK-PAGE-READ)
	(DISPATCH TRANSPORT MD)


(start-dispatch 5 0)
d-structure-info
	(p-bit r-bit)				;one-q-forward

d-find-structure-header
	(fsh-search-loop)			;one-q-forward

d-verify-accumulator-simple			;Simple verifications of accumulator contents
						;to detect dangerous types being left in accumulators
	(n-bit p-bit illop)			;one-q-forward


CAR-PRE-DISPATCH 
	(P-BIT INHIBIT-XCT-NEXT-BIT TRAP)	;ONE-Q-FORWARD


CAR-PRE-DISPATCH-DIRECT
	(P-BIT  TRAP)	;ONE-Q-FORWARD
CARCDR-DISPATCH-DIRECT
	(P-BIT  CARCDR-NOT-LIST)	;ONE-Q-FORWARD







QSLQRY	((VMA-START-READ) ADD A-Q M-array-origin)		;Q-LIST ARRAY
	(CHECK-PAGE-READ)			;NO TRANSPORT SINCE STORING AND JUST
	((WRITE-MEMORY-DATA-START-WRITE)	;TOUCHED HEADER AND DON'T ALLOW ONE-Q-FORWARD
		SELECTIVE-DEPOSIT READ-MEMORY-DATA Q-ALL-BUT-TYPED-POINTER A-T)
	(CHECK-PAGE-WRITE)
	(GC-WRITE-TEST)
        (popj)

;NEEDS TRANSPORTER HACKERY HERE IF ONE-Q-FORWARD S IN ARRAY-LEADERS ARE TO BE SUPPORTED.
XSALDR-AREFI

d-trans-old
	(trans-old-copy)	;one-q-forward

;Enter here for one-q-forward.  Already transported if was old-space.
TRANS-OQF
	(JUMP-IF-BIT-SET (BYTE-FIELD 1 3) READ-I-ARG TRANS-DROP-THROUGH) ;IGNORE OQF IF JUST
	(JUMP-XCT-NEXT TRANS-INVZ)					 ;CHECKING CDR CODE
       (CALL-IF-BIT-SET (BYTE-FIELD 1 2) READ-I-ARG ILLOP)	;BARF IF TRANSPORT-HEADER

d-scavenge-word

	(p-bit r-bit)				       ;one-q-forward