Enable devirtualization opportunities by using the final specifier (C++11)

* Declaring CCoinsViewErrorCatcher final enables devirtualization of two calls
* Declaring CReserveKey final enables devirtualization of one call

src/init.cpp

@@ -133,7 +133,7 @@ bool ShutdownRequested()
  * chainstate, while keeping user interface out of the common library, which is shared
  * between bitcoind, and bitcoin-qt and non-server tools.
 */
-class CCoinsViewErrorCatcher : public CCoinsViewBacked
+class CCoinsViewErrorCatcher final : public CCoinsViewBacked
 {
 public:
     CCoinsViewErrorCatcher(CCoinsView* view) : CCoinsViewBacked(view) {}

src/wallet/wallet.h

@@ -1135,7 +1135,7 @@ public:
 };
 
 /** A key allocated from the key pool. */
-class CReserveKey : public CReserveScript
+class CReserveKey final : public CReserveScript
 {
 protected:
     CWallet* pwallet;