Fix display-to-string

part of darcs patch Wed Sep 21 19:40:54 EEST 2005  Martin Gasbichler <gasbichl@informatik.uni-tuebingen.de>

scheme/utils.scm

@@ -1,12 +1,12 @@
 (define (display-to-string val)
   (let ((exp-port (open-output-string)))
-    (display exp exp-port)
+    (display val exp-port)
     (get-output-string exp-port)))
 
 ;;expression as string
-(define (write-to-string exp)
+(define (write-to-string val)
   (let ((exp-port (open-output-string)))
-    (write exp exp-port)
+    (write val exp-port)
     (get-output-string exp-port)))
 
 (define (on/off-option-processor name)