Add comment for undef of "interface"

src/ChangeLog

+2012-10-15  Daniel Colascione  <dancol@dancol.org>
+
+	* dbusbind.c: Add comment explaining reason for previous change.
+
 2012-10-15  Martin Rudalics  <rudalics@gmx.at>
 
 	* window.c (Fwindow_end): Rewrite check whether cached position

src/dbusbind.c

@@ -32,6 +32,10 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #define DBUS_NUM_MESSAGE_TYPES 5
 #endif
 
+
+/* Some platforms define the symbol "interface", but we want to use it
+ * as a variable name below.  */
+
 #ifdef interface
 #undef interface
 #endif