krb5: include config.h before string.h

Solaris requires __EXTENSIONS__ to be defined before including string.h so that
the strnlen() prototype is visible

lib/krb5/aname_to_localname.c

@@ -31,11 +31,12 @@
  * SUCH DAMAGE.
  */
 
-#include <string.h>
 #include "krb5_locl.h"
 #include "an2ln_plugin.h"
 #include "db_plugin.h"
 
+#include <string.h>
+
 /* Default plugin (DB using binary search of sorted text file) follows */
 static krb5_error_code KRB5_LIB_CALL an2ln_def_plug_init(krb5_context, void **);
 static void KRB5_LIB_CALL an2ln_def_plug_fini(void *);