Removed features.h test.

* configure.in, config.h.in, gdk/gdkimage.c:
        Removed features.h test.

        * gdk/gdkdnd.c:
        Guard public functions against NULL pointer derefs.

gdk/x11/gdkimage-x11.c

@@ -25,9 +25,6 @@
 #ifndef _XOPEN_SOURCE
 #  define _XOPEN_SOURCE 1
 #endif
-#ifdef HAVE_FEATURES_H
-#  include <features.h>
-#endif
 
 #include <stdlib.h>
 #include <sys/types.h>