desktop-shell: Avoid spurious configure events for xdg-shell activation

This is a minor re-work of how we de-activate and activate the surfaces
in desktop-shell. As activate() is being used for handling keyboard
input events, this basically rectifies that such that  activation
happens only if the passed surface is different from the currently
focused surface.

Fixes: #593

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

desktop-shell/shell.c

@@ -3678,16 +3678,18 @@ activate(struct desktop_shell *shell, struct weston_view *view,
 
 	weston_view_activate_input(view, seat, flags);
 
-	if (shseat && shseat->focused_surface) {
+	if (shseat && shseat->focused_surface &&
+	    shseat->focused_surface != main_surface) {
 		struct shell_surface *current_focus =
 			get_shell_surface(shseat->focused_surface);
 		assert(current_focus);
 		shell_surface_deactivate(current_focus);
 	}
 
-	if (shseat)
-		shseat->focused_surface = main_surface;
+	if (shseat && shseat->focused_surface != main_surface) {
 		shell_surface_activate(shsurf);
+		shseat->focused_surface = main_surface;
+	}
 
 	state = ensure_focus_state(shell, seat);
 	if (state == NULL)