T: bugfix: vertical tick was off by 1 pixel

The problem was visible when DL MCS was set to 20
(do a ping -c 192.172.0.1 -i0.2 to get it). The dots
were not plotted at the exact line of the tick mark.

Not sure the fix is always correct.

No big deal anyway.

common/utils/T/tracer/gui/xy_plot.c

@@ -70,7 +70,7 @@ static void paint(gui *_gui, widget *_this)
  */
     char v[64];
     int vwidth, dummy;
-    float x = (k * ticstep - allocated_xmin) /
+    int x = (k * ticstep - allocated_xmin) /
             (allocated_xmax - allocated_xmin) *
             (allocated_plot_width - 1);
     x_draw_line(g->x, g->xwin, FOREGROUND_COLOR,
@@ -112,7 +112,7 @@ static void paint(gui *_gui, widget *_this)
   for (k = kmin; k <= kmax; k++) {
     char v[64];
     int vwidth, dummy;
-    float y = (k * ticstep - allocated_ymin) /
+    int y = (k * ticstep - allocated_ymin) /
             (allocated_ymax - allocated_ymin) *
             (allocated_plot_height - 1);
     sprintf(v, "%g", k * ticstep);