Change the logic such that if AppendHandler::execute detects an error, it
returns right away.  That means that there's no possibility of detecting two
errors or detecting an error and then having that error condition removed or
anything like that.  It also means that I don't need to test for success in
the part that actually does the message creation because I know that it will
only get there if the process was a success.
Add the ability to get coverage data and start to use the coverage data to
guide the creation of the unit tests.