build: do the right thing with config.h (bgo #644664)

1) it shouldn't be included in headers
2) it should be the first thing included in source files
3) it's needed for getting translation right

src/nm-activation-request.c

@@ -19,6 +19,8 @@
  * Copyright (C) 2007 - 2008 Novell, Inc.
  */
 
+#include "config.h"
+
 #include <string.h>
 #include <stdlib.h>
 #include <sys/wait.h>