[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/rpcrawtransaction.cpp

@@ -527,9 +527,9 @@ Value signrawtransaction(const Array& params, bool fHelp)
 
 Value sendrawtransaction(const Array& params, bool fHelp)
 {
-    if (fHelp || params.size() < 1 || params.size() > 1)
+    if (fHelp || params.size() < 1 || params.size() > 2)
         throw runtime_error(
-            "sendrawtransaction <hex string>\n"
+            "sendrawtransaction <hex string> [allowhighfees=false]\n"
             "Submits raw transaction (serialized, hex-encoded) to local node and network.");
 
     // parse hex string from parameter
@@ -537,6 +537,10 @@ Value sendrawtransaction(const Array& params, bool fHelp)
     CDataStream ssData(txData, SER_NETWORK, PROTOCOL_VERSION);
     CTransaction tx;
 
+    bool fOverrideFees = false;
+    if (params.size() > 1)
+        fOverrideFees = params[1].get_bool();
+
     // deserialize binary data stream
     try {
         ssData >> tx;
@@ -554,7 +558,7 @@ Value sendrawtransaction(const Array& params, bool fHelp)
         if (!fHave) {
             // push to local node
             CValidationState state;
-            if (!mempool.accept(state, tx, false, NULL))
+            if (!mempool.accept(state, tx, false, NULL, !fOverrideFees))
                 throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX rejected"); // TODO: report validation state
         }
     }