Remove signal DoubleSpendDetected, use function

Also removes the need for forward reference to RelayableRespend.

src/main.h

@@ -108,8 +108,8 @@ struct CNodeStateStats;
 
 struct CBlockTemplate;
 
-/** Set up internal signal handlers **/
-void RegisterInternalSignals();
+/** Initialize respend bloom filter **/
+void InitRespendFilter();
 
 /** Register a wallet to receive updates from core */
 void RegisterWallet(CWalletInterface* pwalletIn);