GH-1726 better failure detection for updates

Instead of just checking if the new version started, make sure
it is able to write its IPC key to a file and then use the key
to connect to the process.

application/UpdateController.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include <QString>
+#include <QList>
+#include <updater/GoUpdate.h>
+
+class QWidget;
+
+class UpdateController
+{
+public:
+	UpdateController(QWidget * parent, const QString &root, const QString updateFilesDir, GoUpdate::OperationList operations);
+	void installUpdates();
+
+private:
+	void fail();
+	bool rollback();
+
+private:
+	QString m_root;
+	QString m_updateFilesDir;
+	GoUpdate::OperationList m_operations;
+	QWidget * m_parent;
+
+	struct BackupEntry
+	{
+		// path where we got the new file from
+		QString update;
+		// path of what is being actually updated
+		QString original;
+		// path where the backup of the updated file was placed
+		QString backup;
+	};
+	QList <BackupEntry> m_replace_backups;
+	QList <BackupEntry> m_delete_backups;
+	enum Failure
+	{
+		Replace,
+		Delete,
+		Start,
+		Nothing
+	} m_failedOperationType = Nothing;
+	QString m_failedFile;
+};