So, the workaround is super ugly but fairly simple to implement.  It hinges on the fact that while the debug log gets truncated, the values that are passed back to your test code aren't.

I accumulate a String with various debugging output, as well as regular output from the run.  In my case I was e-mailing various admins the results of the run as this was a batch job, so I just used the same string.

1.  in my code I changed all my system.debug()'s to a call to addMsg() which is:

public void addMsg(String s) {system.debug(s); emailMsg = emailMsg + '\n' + DateTime.now() + ' - ' + s;}

2. For the main function I was calling to kick off the test, I changed it from returning a void to returning a String.

3. At the end of the run, it returns the accumulated emailMsg as the String value.

4. In the testing code below, uncomment the system.assert() call.  The assertion will fail, and then you'll get the entire string value.  Just issuing a system.debug(xxx) wouldn't do the trick.

In my testing code:

		// Instantiate the class which runs the code.
		test.startTest();
		Client_Status_History_Review CSHR = new Client_Status_History_Review();
		//
		// Because the production system has so many validations and workflow rules set up on Client Status History records, we can't 
		// see the entire debug log if something goes wrong in order to see our error messages.  So, the only way we can get them is
		// to return them to the calling test function.  And, even then they won't show up in the debug log unless we can force it somehow.
		// One way to force it is to have an assertion fail with the text of the Debug log in the assertion.
		String xxx = CSHR.doReview();
		// The following fails and gives us our Debug log.
		// In real testing we don't want this line as we would never go on to the testing assertions below.
		//system.assertEquals('',xxx);
		test.stopTest();

So, this was kludgy, but it was the only way I could find to get my full debug output.  I'd love to hear other solutions if people any any.   Best, Steve.