Add gdk-pixbuf include dir (split out in gtk+-2.21).

--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,4 +1,4 @@
-INCLUDE_DIRECTORIES( ${OPENSYNC_INCLUDE_DIRS} ${GTK2_INCLUDE_DIRS} ${LIBGLADE_INCLUDE_DIRS} ${LIBXML2_INCLUDE_DIRS} )
+INCLUDE_DIRECTORIES( ${OPENSYNC_INCLUDE_DIRS} ${GTK2_INCLUDE_DIRS} ${LIBGLADE_INCLUDE_DIRS} ${LIBXML2_INCLUDE_DIRS} /usr/include/gdk-pixbuf-2.0 )
 LINK_DIRECTORIES( ${OPENSYNC_LIBRARY_DIRS} ${GTK2_LIBRARY_DIRS} ${LIBGLADE_LIBRARY_DIRS} ${LIBXML2_LIBRARY_DIRS} )
 
 SET( multisyncgui_SRCS