Add function to convert CValidationState to a human-readable message

It is necessary to be able to concisely log a validation state.
Convert CValidationState to a human-readable message for logging.

src/main.cpp

@@ -778,6 +778,14 @@ CAmount GetMinRelayFee(const CTransaction& tx, unsigned int nBytes, bool fAllowF
     return nMinFee;
 }
 
+/** Convert CValidationState to a human-readable message for logging */
+static std::string FormatStateMessage(const CValidationState &state)
+{
+    return strprintf("%s%s (code %i)",
+        state.GetRejectReason(),
+        state.GetDebugMessage().empty() ? "" : ", "+state.GetDebugMessage(),
+        state.GetRejectCode());
+}
 
 bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransaction &tx, bool fLimitFree,
                         bool* pfMissingInputs, bool fRejectAbsurdFee)