Reworking thread termination logic.

Turns out the finish methods weren't called correctly, caused by a
mess up with method names which all sounded too similar and the wrong
one ended up being called. I've reworked this by changing the
thread/writer/reader interfaces, which actually also simplifies them
by getting rid of the requirement for writer backends to call their
parent methods (i.e., less opportunity for errors).

This commit also includes the following (because I noticed the problem
above when working on some of these):

     - The ASCII log writer now includes "#start <timestamp>" and
      "#end <timestamp> lines in the each file. The latter supersedes
      Bernhard's "EOF" patch.

      This required a number of tests updates. The standard canonifier
      removes the timestamps, but some tests compare files directly,
      which doesn't work if they aren't printing out the same
      timestamps (like the comm tests).

     - The above required yet another change to the writer API to
       network_time to methods.

     - Renamed ASCII logger "header" options to "meta".

     - Fixes #763 "Escape # when first character in log file line".

All btests pass for me on Linux FC15. Will try MacOS next.

src/threading/MsgThread.h

@@ -189,39 +189,45 @@ protected:
 	 *
 	 * This is method is called regularly by the threading::Manager.
 	 *
-	 * Can be overriden in derived classed to hook into the heart beat,
-	 * but must call the parent implementation. Note that this method is
-	 * always called by the main thread and must not access data of the
-	 * child thread directly. See DoHeartbeat() if you want to do
-	 * something on the child-side.
+	 * Can be overriden in derived classed to hook into the heart beat
+	 * sending, but must call the parent implementation. Note that this
+	 * method is always called by the main thread and must not access
+	 * data of the child thread directly. Implement OnHeartbeat() if you
+	 * want to do something on the child-side.
 	 */
 	virtual void Heartbeat();
 
-	/**
-	 * Overriden from BasicThread.
-	 *
+	/** Flags that the child process has finished processing. Called from child.
 	 */
-	virtual void Run();
-	virtual void OnStop();
+	void Finished();
+
+	/** Internal heartbeat processing. Called from child.
+	 */
+	void HeartbeatInChild();
 
 	/**
 	 * Regulatly triggered for execution in the child thread.
 	 *
-	 * When overriding, one must call the parent class' implementation.
-	 *
 	 * network_time: The network_time when the heartbeat was trigger by
 	 * the main thread.
 	 *
 	 * current_time: Wall clock when the heartbeat was trigger by the
 	 * main thread.
 	 */
-	virtual bool DoHeartbeat(double network_time, double current_time);
+	virtual bool OnHeartbeat(double network_time, double current_time) = 0;
 
 	/** Triggered for execution in the child thread just before shutting threads down.
 	 *  The child thread should finish its operations and then *must*
 	 *  call this class' implementation.
 	 */
-	virtual bool DoFinish();
+	virtual bool OnFinish(double network_time) = 0;
+
+	/**
+	 * Overriden from BasicThread.
+	 *
+	 */
+	virtual void Run();
+	virtual void OnStop();
 
 private:
 	/**