Clean up MFS a bit:

- Remove unused includes.
 - Add include guards to headers.
 - Use unsigned variables in case they're never going to hold a negative
   value. This causes GCC's complaints to disappear and should make flexelint
   a lot happier, too.
 - Make functions private when they're used only within a module.
 - Remove unused variables.
 - Add casts where appropriate.

servers/mfs/table.c

@@ -6,8 +6,6 @@
 #define _TABLE
 
 #include "fs.h"
-#include <minix/callnr.h>
-#include <minix/com.h>
 #include "inode.h"
 #include "buf.h"
 #include "super.h"