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.

include/treaty.h

@@ -34,6 +34,9 @@
 #ifndef TREATY_H
 #define TREATY_H
 
+#include <time.h>
+#include "types.h"
+
 struct trtstr {
     short ef_type;
     natid trt_cna;		/* proposer */