Some functions (e.g. getpwnam()/getgrnam()) will return an error but not set errno. In this case there's no use in appending strerror(), which will be "Success". This is confusing since an error has just been reported.
At least in the examples above, an error with no errno set just means "missing" and our current error message already conveys that.
There was a lot of extra boilerplate involved in setting up pipes so that is now automated.
In some cases testing with multiple children is useful so allow that as well.
The prior behavior was to throw an exception but this was not very helpful when something unexpected happened. Better to at least emit the error message even if the error code is not very helpful.
Improve on 7794ab50 by including the build flag files directly into the Makefile as dependencies (even though they are not includes). This simplifies some of the rsync logic and allows make to do what it does best.
Also split build flag files into test, harness, and build to reduce rebuilds. Test flags are used to build test.c, harness flags are used to build the rest of the files in the test harness, and build flags are used for the files that are not directly involved in testing.
Low-level functions only include stack trace in test builds while higher-level functions ship with stack trace built-in. Stack traces include all parameters passed to the function but production builds only create the parameter list when the log level is set high enough, i.e. debug or trace depending on the function.
