worker: add basic test to ensure child processes are managed well This should catch the bug fixed by "worker: ignore meaningless exit status indication returned by os.waitpid()." Before, worker.py was untested since test repositories are relatively small.

color: rename '_styles' to '_defaultstyles' for clarity This should make it clear the dict is only used for new config. Extensions should not modify it directly anyway since we have 'extraloader' logic for loading '_styles' too.