[glibmm] Gio::Application::custom_class_init(): Update a comment

[Kjell Ahlstedt <kjellahl src gnome org>]

commit e1751f95986a216b0c4d202b897e9c6ea4fe2669
Author: Kjell Ahlstedt <kjellahlstedt gmail com>
Date:   Wed Sep 27 16:11:07 2017 +0200

    Gio::Application::custom_class_init(): Update a comment
    
    The private custom_class_init() method is still needed, but the
    reason is no longer that the deprecated g_type_init() must be called.

 gio/src/application.ccg |    6 ++++--
 gio/src/application.hg  |    6 ++----
 2 files changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/gio/src/application.ccg b/gio/src/application.ccg
index ca57852..d85ae8d 100644
--- a/gio/src/application.ccg
+++ b/gio/src/application.ccg
@@ -272,9 +272,11 @@ Application::custom_class_init()
 
 Application::Application(const Glib::ustring& application_id, Flags flags)
 : // Mark this class as non-derived to allow C++ vfuncs to be skipped.
+  // GApplication complains about "" but allows nullptr, so we avoid passing "".
   Glib::ObjectBase(nullptr),
-  Glib::Object(Glib::ConstructParams(custom_class_init(), "application_id",
-    Glib::c_str_or_nullptr(application_id), "flags", ((GApplicationFlags)(flags)), nullptr))
+  Glib::Object(Glib::ConstructParams(custom_class_init(),
+    "application_id", Glib::c_str_or_nullptr(application_id),
+    "flags", static_cast<GApplicationFlags>(flags), nullptr))
 {
 }
 
diff --git a/gio/src/application.hg b/gio/src/application.hg
index 5f414a9..7767854 100644
--- a/gio/src/application.hg
+++ b/gio/src/application.hg
@@ -421,10 +421,8 @@ protected:
   _WRAP_VFUNC(void dbus_unregister(const Glib::RefPtr<DBus::Connection>& connection, const Glib::ustring& 
object_path), "dbus_unregister")
 
 private:
-  /** This is just a way to call Glib::init() (which calls g_type_init()) before
-   * calling application_class_.init(), so that
-   * g_application_get_type() will always succeed.
-   * See https://bugzilla.gnome.org/show_bug.cgi?id=639925
+  /** This is just a way to call Glib::init() before calling a Glib::Object ctor,
+   * so that glibmm's GQuarks are created before they are used.
    */
   const Glib::Class& custom_class_init();