Fix some threading things and add additional thread unittests

- Fix thread name reset on start()
- Fully reset thread state on kill()
- Add unittests to check for correct object states under various circumstances

src/threading/thread.h

@@ -81,9 +81,10 @@ public:
 	/*
 	 * Waits for thread to finish.
 	 * Note:  This does not stop a thread, you have to do this on your own.
-	 * Returns immediately if the thread is not started.
+	 * Returns false immediately if the thread is not started or has been waited
+	 * on before.
 	 */
-	void wait();
+	bool wait();
 
 	/*
 	 * Returns true if the calling thread is this Thread object.
@@ -140,15 +141,14 @@ protected:
 
 private:
 	void *m_retval;
+	bool m_joinable;
 	Atomic<bool> m_request_stop;
 	Atomic<bool> m_running;
-	Mutex m_continue_mutex;
+	Mutex m_mutex;
 
 	threadid_t m_thread_id;
 	threadhandle_t m_thread_handle;
 
-	void cleanup();
-
 	static ThreadStartFunc threadProc;
 
 #ifdef _AIX