Break inclusion cycle: prototypes.h and commands.h included each

other.  Ensure headers in include/ can be included in any order
(except for econfig-spec.h, which is special).  New header types.h to
help avoid inclusion cycles.  Sort include directives.  Remove some
superflous includes.

src/lib/common/xundump.c

@@ -48,14 +48,10 @@
 
 #include <config.h>
 
-#include <stdio.h>
-#include <stdlib.h>
-
 #include <ctype.h>
-#include <string.h>
 #include <stdarg.h>
+#include <stdio.h>
 #include <time.h>
-
 #include "file.h"
 #include "match.h"
 #include "nsc.h"