headers: include-what-you-use fixes

Usage of includes are set up the way found to be in use, with a help of
magnificent utility.

http://code.google.com/p/include-what-you-use/

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

src/sort.c

@@ -15,15 +15,11 @@
 ** along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-#ifdef HAVE_CONFIG_H
 #include <config.h>
-#endif
-
-#include <stdlib.h>
-#include <stdio.h>
-#include <string.h>
-#include <errno.h>
 #include <err.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
 
 #include "dhcpd-pools.h"