Issue #407: fix incorrect casts in calls to ctype functions (isdigit and isspace) so we don't crash when asserts are enabled on certain platforms and characters > 128 are parsed.

json_tokener.c

@@ -295,7 +295,7 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
 
     case json_tokener_state_eatws:
       /* Advance until we change state */
-      while (isspace((int)c)) {
+      while (isspace((unsigned char)c)) {
 	if ((!ADVANCE_CHAR(str, tok)) || (!PEEK_CHAR(c, tok)))
 	  goto out;
       }