Have MIDAS define the right constant area start symbol.

When building MUDDLE, I was seeing various unresolved symbols of the
form "$   42". These are used by MIDAS when it wants to refer to
something in a CONSTANTS area, but doesn't know the location at assembly
time (for example, because it's the other side of a LOC X where X is a
global). At the start of a CONSTANTS area, MIDAS should define this
symbol as .; however, it was defining it with the wrong name.

There's a special case in RPWRD1 to output these symbols as squoze
rather than symbol table numbers -- but the code in CNST2 that defines
the symbol was using PDEFPT, which always outputs the number.
Modify it to output the squoze instead.

<mdl.int>/midas.323

@@ -3857,7 +3857,10 @@ CNST2:	MOVEI D,(T)	;STE IDX IN D FOR OUTSM0
 	MOVE SYM,(T)	;GET NAME OF AREA
 	TLC SYM,400000#LCUDF	;CLEAR LCUDF, SET HALF-KILL
 	TRNE FF,FRGLOL
-	PUSHJ P,PDEFPT	;DEFINE SYM FOR BEGINNING OF CONSTANTS AREA
+	JRST [	MOVEI A,CDEFPT	;Define sym for beginning of constants area
+		PUSHJ P,P7X
+		PUSHJ P,OUTSM	;As PDEFPT but punch squoze (see RPWRD1)
+		JRST .+1]
 	MOVE A,CONTBA
 CNSTH:	CAML A,PLIM
 	 JRST CNSTA	;THRU