[gtk+] porting guide: Update to mention GDK_KEY_ transition

[Colin Walters <walters src gnome org>]

commit e08c43faf45540eea0f024818d8b2ff30a355b82
Author: Colin Walters <walters verbum org>
Date:   Wed Sep 8 18:25:52 2010 -0400

    porting guide: Update to mention GDK_KEY_ transition

 docs/reference/gtk/migrating-2to3.xml |   14 ++++++++++++++
 1 files changed, 14 insertions(+), 0 deletions(-)
---
diff --git a/docs/reference/gtk/migrating-2to3.xml b/docs/reference/gtk/migrating-2to3.xml
index b966a8e..1d003e2 100644
--- a/docs/reference/gtk/migrating-2to3.xml
+++ b/docs/reference/gtk/migrating-2to3.xml
@@ -114,6 +114,20 @@
   </section>
 
   <section>
+    <title>Replace GDK_&lt;keyname&gt; with GDK_KEY_&lt;keyname&gt;</title>
+
+    <para>
+      Key constants have gained a <literal>_KEY</literal>, prefix.
+      For example, <literal>GDK_a</literal> is now
+      <literal>GDK_KEY_a</literal>.  In GTK+ 2, the old names continue
+      to be available.  In GTK+ 3 however, the old names will require
+      an explicit include of the
+      <literal>gdkkeysyms-compat.h</literal> header.
+    </para>
+
+  </section>
+
+  <section>
     <title>Use cairo for drawing</title>
     <para>
       In GTK+ 3, the GDK drawing API (which closely mimics the X