Docs: use // for comments in examples

Without sgml mode, we can't escape /* as /* anymore,
so just switch to // for comments in examples.

gtk/gtkdialog.c

@@ -100,14 +100,14 @@
  *
  * An example for simple GtkDialog usage:
  * |[<!-- language="C" -->
- * /&ast; Function to open a dialog box with a message &ast;/
+ * // Function to open a dialog box with a message
  * void
  * quick_message (GtkWindow *parent, gchar *message)
  * {
  *  GtkWidget *dialog, *label, *content_area;
  *  GtkDialogFlags flags;
  *
- *  /&ast; Create the widgets &ast;/
+ *  // Create the widgets
  *  flags = GTK_DIALOG_DESTROY_WITH_PARENT;
  *  dialog = gtk_dialog_new_with_buttons ("Message",
  *                                        parent,
@@ -118,15 +118,14 @@
  *  content_area = gtk_dialog_get_content_area (GTK_DIALOG (dialog));
  *  label = gtk_label_new (message);
  *
- *  /&ast; Ensure that the dialog box is destroyed when the user
- *  responds &ast;/
+ *  // Ensure that the dialog box is destroyed when the user responds
  *
  *  g_signal_connect_swapped (dialog,
  *                            "response",
  *                            G_CALLBACK (gtk_widget_destroy),
  *                            dialog);
  *
- *  /&ast; Add the label, and show everything we’ve added &ast;/
+ *  // Add the label, and show everything we’ve added
  *
  *  gtk_container_add (GTK_CONTAINER (content_area), label);
  *  gtk_widget_show_all (dialog);