scroll by one line in textlist

to scroll by only one line, hold CONTROL key and scroll with
mouse wheel

common/utils/T/tracer/view/textlist.c

@@ -89,6 +89,8 @@ static void scroll(void *private, gui *g,
   int number_of_lines;
   int new_line;
   int inc;
+  int *d = notification_data;
+  int key_modifiers = *d;
 
   if (pthread_mutex_lock(&this->lock)) abort();
 
@@ -96,6 +98,7 @@ static void scroll(void *private, gui *g,
   inc = 10;
   if (inc > visible_lines - 2) inc = visible_lines - 2;
   if (inc < 1) inc = 1;
+  if (key_modifiers & KEY_CONTROL) inc = 1;
   if (!strcmp(notification, "scrollup")) inc = -inc;
 
   new_line = start_line + inc;