Add missing include so include file compiles cleanly on its own.

Author: bmomjian

src/include/commands/tablecmds.h

@@ -14,6 +14,7 @@
 #ifndef TABLECMDS_H
 #define TABLECMDS_H
 
+#include "access/htup.h"
 #include "nodes/parsenodes.h"
 #include "storage/lock.h"
 #include "utils/relcache.h"