[gtkmm] Pixbuf: Comment out AlphaMode.

[Murray Cumming <murrayc src gnome org>]

commit 1771083f18120d8ba15cdbdc2e98629086389b1d
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Apr 27 14:13:57 2017 +0200

    Pixbuf: Comment out AlphaMode.
    
    We don't use it in our API. It seems to be used only inside the
    gdk-pixbuf library.

 gdk/src/pixbuf.hg |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/gdk/src/pixbuf.hg b/gdk/src/pixbuf.hg
index 82f13d0..2f0a296 100644
--- a/gdk/src/pixbuf.hg
+++ b/gdk/src/pixbuf.hg
@@ -56,9 +56,6 @@ class Pixbuf
   _IGNORE(gdk_pixbuf_ref, gdk_pixbuf_unref,  gdk_pixbuf_non_anim_new)
 
 protected:
-  _WRAP_ENUM(AlphaMode, GdkPixbufAlphaMode)
-  _WRAP_ENUM(Rotation, GdkPixbufRotation)
-
   /** Transfers image data from a Cairo::Surface and converts it to an RGB(A)
    * representation inside a Gdk::Pixbuf. This allows you to efficiently read
    * individual pixels from cairo surfaces.
@@ -82,6 +79,9 @@ protected:
 
 
 public:
+  // Used only internally in gdk-pixbuf: _WRAP_ENUM(AlphaMode, GdkPixbufAlphaMode)
+  _WRAP_ENUM(Rotation, GdkPixbufRotation)
+
   using SlotDestroyData = sigc::slot<void(const guint8*)>;
 
   /** Transfers image data from a Cairo::Surface and converts it to an RGB(A)