fix string-titlecase on special-casing characters

original commit: 0ae58f75bcf76fb41e571579a81ab2080379455c

LOG

@@ -1027,3 +1027,6 @@
     cpnanopass.ss, x86_64.ss, x86.ss, foreign2.c, foreign.ms
 - added initialization of seginfo sorted and trigger_ephemerons fields.
     segment.c
+- fix `string-titlecase` on special-casing characters like #\xDF and
+   #\xFB00
+    5_4.ss, 5_4.ms

mats/5_4.ms

@@ -1162,6 +1162,10 @@
   (test (string-titlecase "r6rs") "R6rs") ; this example appears to be wrong in R6RS (Sept 2007 version)
   (test (string-titlecase "R6RS") "R6rs") ; this one, too
 
+  (test (string-titlecase "stra \xDF;e") "Stra Sse")
+  (test (string-titlecase "one \xFB00;e") "One Ffe")
+  (test (string-titlecase "one\xFB00;e") "One\xFB00;e")
+
   (test (string-downcase "A\x3A3;'x") "a\x3C3;'x") ; ' is a MidLetter
 
   (test (string-ci<? "a" "Z") #t)

s/5_4.ss

@@ -403,9 +403,11 @@
           (define (trans s i c seen-cased? ac)
             (if seen-cased?
                 (trans1 s i ($str-downcase c) #t ac)
-                (if ($char-cased? c)
-                    (trans1 s i ($str-titlecase c) #t ac)
-                    (trans1 s i c #f ac))))
+                (let ([tc ($str-titlecase c)])
+                  (if (or ($char-cased? c)
+                          (not (eqv? c tc)))
+                      (trans1 s i tc #t ac)
+                      (trans1 s i c #f ac)))))
           ; NB: if used as a pattern for word breaking, take care not to break between CR & LF (WB3)
           ; NB: and between regional-indicators (WB13c).  also take care not to let handling of WB6 and
           ; NB: WB7 here prevent breaks in, e.g., "a." when not followed by, e.g., another letter.