Combine two tests that had identical names (one shadowed the other).
"not a in b" -> "a not in b"
One statement per line.
Break a few lines that were too long.
Remove trailing whitespace.

Actually, Task.makeTask already supported subtasks held
in pexConfig.RegistryField, but it was not documented or tested.
Document this and add a test. Also rename a variable to make the
code less confusing.