Auto merge of #1105 - bitcartel:zc.v0.11.2.z6_issue_424, r=ebfull

New private/public key pairs for broadcasting alert messages

Implements #424

Fixes and integrates method of sending alerts as described by upstream here:
- https://gist.github.com/laanwj/0e689cfa37b52bcbbb44

To send an alert:
- Copy private keys into alertkeys.h.
- Modify alert parameters and message found in sendalert.cpp
- Build and run to send the alert e.g. ./zcashd -printtoconsole -sendalert

Tested and verified with local nodes on alpha 6 testnet.

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;
 }