Return improved error message when trying to spend Coinbase coins (#1373).

Extra parameter added to AvailableCoins to include or exclude Coinbase coins.
SelectCoins, used for sending taddr->taddr, will exclude Coinbase coins.

Added qa rpc test and a runtime parameter -regtestprotectcoinbase to enforce
the coinbase->zaddr consensus rule in regtest mode.

src/chainparams.cpp

@@ -336,6 +336,11 @@ CChainParams &Params(CBaseChainParams::Network network) {
 void SelectParams(CBaseChainParams::Network network) {
     SelectBaseParams(network);
     pCurrentParams = &Params(network);
+
+    // Some python qa rpc tests need to enforce the coinbase consensus rule
+    if (network == CBaseChainParams::REGTEST && mapArgs.count("-regtestprotectcoinbase")) {
+        regTestParams.SetRegTestCoinbaseMustBeProtected();
+    }
 }
 
 bool SelectParamsFromCommandLine()