fix immuatable? on hash-table

svn: r4419

src/mzscheme/src/list.c

@@ -870,7 +870,8 @@ immutablep (int argc, Scheme_Object *argv[])
 	       || SCHEME_VECTORP(v)
 	       || SCHEME_BYTE_STRINGP(v)
 	       || SCHEME_CHAR_STRINGP(v)
-	       || SCHEME_BOXP(v)))
+	       || SCHEME_BOXP(v)
+	       || SCHEME_HASHTP(v)))
 	  ? scheme_true
 	  : scheme_false);
 }