Static assertion that standard and network min tx versions are consistent.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

src/primitives/transaction.h

@@ -11,6 +11,7 @@
 #include "script/script.h"
 #include "serialize.h"
 #include "uint256.h"
+#include "consensus/consensus.h"
 
 #include <boost/array.hpp>
 
@@ -313,6 +314,9 @@ public:
     static const int32_t MIN_CURRENT_VERSION = 1;
     static const int32_t MAX_CURRENT_VERSION = 2;
 
+    static_assert(MIN_CURRENT_VERSION >= MIN_TX_VERSION,
+                  "standard rule for tx version should be consistent with network rule");
+
     // The local variables are made const to prevent unintended modification
     // without updating the cached hash value. However, CTransaction is not
     // actually immutable; deserialization and assignment are implemented,