Print end of line after warning/error message
Add more suite examples

Now it is obvious mixing different suites is possible (though not
advisable).
Fix debug message
Fix crash when registering tests in not last suite

Registering a test in a suite that was not the last one added may have
caused a crash.
Minor cleanup
Rename global variable

Not it is explicit that the tests are stored in a global linked list and
where this global variable is used.