Make SendEvent callable from all threads

This commit refactors the SendEvent call and moves it from the Input
ReaderBackend to to MsgThread. This allows all other types of threads
to access this functionality.

This necessitated a few more changes. Most importantly, one of the
ValueToVal methods was moved over to SerialTypes. Whereit arguably
belongs - there was nothing that was input-framework specific in
that method - and the functionality could come in useful in a number
of cases.

src/threading/MsgThread.cc

@@ -126,6 +126,31 @@ private:
 
 }
 
+// An event that the child wants to pass into the main event queue
+class SendEventMessage final : public OutputMessage<MsgThread> {
+public:
+	SendEventMessage(MsgThread* thread, const char* name, const int num_vals, Value* *val)
+		: OutputMessage<MsgThread>("SendEvent", thread),
+	  name(copy_string(name)), num_vals(num_vals), val(val) {}
+
+	~SendEventMessage() override	{ delete [] name; }
+
+	bool Process() override
+		{
+		bool success = thread_mgr->SendEvent(Object(), name, num_vals, val);
+
+		if ( ! success )
+			reporter->Error("SendEvent for event %s failed", name);
+
+		return true; // We do not want to die if sendEvent fails because the event did not return.
+		}
+
+private:
+	const char* name;
+	const int num_vals;
+	Value* *val;
+};
+
 ////// Methods.
 
 Message::~Message()
@@ -363,6 +388,11 @@ void MsgThread::SendOut(BasicOutputMessage* msg, bool force)
 	flare.Fire();
 	}
 
+void MsgThread::SendEvent(const char* name, const int num_vals, Value* *vals)
+	{
+	SendOut(new SendEventMessage(this, name, num_vals, vals));
+	}
+
 BasicOutputMessage* MsgThread::RetrieveOut()
 	{
 	BasicOutputMessage* msg = queue_out.Get();