Revert "Remove signal DoubleSpendDetected, use function"

This reverts commit 0da6b3fd18.

src/init.cpp

@@ -1229,7 +1229,7 @@ bool AppInit2(boost::thread_group& threadGroup)
     LogPrintf("mapAddressBook.size() = %u\n",  pwalletMain ? pwalletMain->mapAddressBook.size() : 0);
 #endif
 
-    InitRespendFilter();
+    RegisterInternalSignals();
     StartNode(threadGroup);
     if (fServer)
         StartRPCThreads();