Explicitly add GIO to the client libs

This prevents a build warning on Fedora 16 of:
   undefined reference to symbol 'g_file_get_basename'
diff --git a/configure.ac b/configure.ac
index 9af8590..2f2cee4 100644
--- a/configure.ac
+++ b/configure.ac
@@ -104,7 +104,7 @@
 if test x$enable_clients == xyes; then
   AC_DEFINE([BUILD_CLIENTS], [1], [Build the Wayland clients])
 
-  PKG_CHECK_MODULES(CLIENT, [wayland-client wayland-egl egl >= 7.10 gl cairo >= 1.10.0 gdk-pixbuf-2.0 glib-2.0 gobject-2.0 xkbcommon])
+  PKG_CHECK_MODULES(CLIENT, [wayland-client wayland-egl egl >= 7.10 gl cairo >= 1.10.0 gdk-pixbuf-2.0 glib-2.0 gobject-2.0 gio-2.0 xkbcommon])
 
   PKG_CHECK_MODULES(POPPLER, [poppler-glib],
 			     [have_poppler=yes], [have_poppler=no])