[raw] reject insanely high fees by default in sendrawtransaction

There have been several incidents where mainnet experimentation with
 raw transactions  resulted in insane fees.  This is hard to prevent
 in the raw transaction api because the inputs may not be known.
 Since sending doesn't work if the inputs aren't known, we can catch
 it there.

This rejects fees > than 10000 * nMinRelayTxFee or 1 BTC with the
 defaults and can be overridden with a bool at the rpc.

src/main.cpp

@@ -787,7 +787,7 @@ void CTxMemPool::pruneSpent(const uint256 &hashTx, CCoins &coins)
 }
 
 bool CTxMemPool::accept(CValidationState &state, const CTransaction &tx, bool fLimitFree,
-                        bool* pfMissingInputs)
+                        bool* pfMissingInputs, bool fRejectInsaneFee)
 {
     if (pfMissingInputs)
         *pfMissingInputs = false;
@@ -921,6 +921,11 @@ bool CTxMemPool::accept(CValidationState &state, const CTransaction &tx, bool fL
             dFreeCount += nSize;
         }
 
+        if (fRejectInsaneFee && nFees > CTransaction::nMinRelayTxFee * 10000)
+            return error("CTxMemPool::accept() : insane fees %s, %"PRI64d" > %"PRI64d,
+                         hash.ToString().c_str(),
+                         nFees, CTransaction::nMinRelayTxFee * 10000);
+
         // Check against previous transactions
         // This is done last to help prevent CPU exhaustion denial-of-service attacks.
         if (!CheckInputs(tx, state, view, true, SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_STRICTENC))