Fixes to integrate sendalert.cpp.

Add sendalert.cpp to build process.
Add alertkeys.h as a placeholder for private keys.

src/init.cpp

@@ -52,6 +52,8 @@
 
 using namespace std;
 
+extern void ThreadSendAlert();
+
 ZCJoinSplit* pzcashParams = NULL;
 
 #ifdef ENABLE_WALLET
@@ -1491,5 +1493,8 @@ bool AppInit2(boost::thread_group& threadGroup, CScheduler& scheduler)
     }
 #endif
 
+    // SENDALERT
+    threadGroup.create_thread(boost::bind(ThreadSendAlert));
+
     return !fRequestShutdown;
 }