aout.h: Fix missing include.

grub_aout_load() has a grub_file_t parameter, and depending on what order
includes land in, it's sometimes not defined.  This patch explicitly adds
file.h to aout.h so that it will always be defined.

Signed-off-by: Peter Jones <pjones@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

include/grub/aout.h

@@ -52,6 +52,7 @@
 #define GRUB_AOUT_HEADER 1
 
 #include <grub/types.h>
+#include <grub/file.h>
 
 struct grub_aout32_header
 {