Avoid some flickering when a new window opens

A new window is by default above all other windows. This means that when we map
it and then *later* move it to the correct place in the stacking order (thanks
to lazy restacking), the window on the top of the stack has to redraw itself.

I noticed this via naughty notifies redrawing themselves after opening a browser
window.

Signed-off-by: Uli Schlachter <psychon@znc.in>

client.c

@@ -628,6 +628,14 @@ client_manage(xcb_window_t w, xcb_get_geometry_reply_t *wgeom, int phys_screen,
     /* Make sure the window is automatically mapped if awesome exits or dies. */
     xcb_change_save_set(globalconf.connection, XCB_SET_MODE_INSERT, w);
 
+    /* Move this window to the bottom of the stack. Without this we would force
+     * other windows which will be above this one to redraw themselves because
+     * this window occludes them for a tiny moment. The next stack_refresh()
+     * will fix this up and move the window to its correct place. */
+    xcb_configure_window(globalconf.connection, w,
+                         XCB_CONFIG_WINDOW_STACK_MODE,
+                         (uint32_t[]) { XCB_STACK_MODE_BELOW});
+
     client_t *c = client_new(globalconf.L);
 
     /* This cannot change, ever. */