app: debug dialog will now advise to update when relevant.

Instead of making the focus on bug reporting, the debug dialog will now
make the focus on updating the application if it is found that one is
not using the last version.
Debug data (backtraces and co.) will still be available and copiable,
but under an expander, and bug report button won't be displayed (i.e.
data will still be available upon request but we don't push anymore
people to submit it directly if they are using old versions of GIMP).

Of course, if you are using the last version (or version check was not
possible), the dialog still stays the same.

(cherry picked from commit 2f379494a7)

app/dialogs/dialogs-constructors.c

@@ -222,7 +222,9 @@ dialogs_critical_get (GimpDialogFactory *factory,
                       GimpUIManager     *ui_manager,
                       gint               view_size)
 {
-  return gimp_critical_dialog_new (_("GIMP Debug"));
+  return gimp_critical_dialog_new (_("GIMP Debug"),
+                                   context->gimp->config->last_known_release,
+                                   context->gimp->config->last_release_timestamp);
 }
 
 GtkWidget *