As a follow on to bpo-46716, the various timeout parameters currently deal with negative values differently in POSIX and Windows.

On POSIX, a negative value is treated the same as 0; check completion and raise TimeoutExpired is still running.

On Windows, the negative value is treated as unsigned and ultimately waits for ~49 days.

While the Windows behavior is obviously wrong and will be fixed internally as part of bpo-46716, that still leaves what to do with timeouts coming from user-space.  The current documentation just states that after `timeout` seconds TimeoutExpired is raised.  A liberal reading of the documentation could lead one to believe any value <=0 would suffice for an "active" check (the POSIX behavior).

OR, the documentation could be amended and negative values are now invalid and apply range checking in the user-facing functions.

Oh, I forgot to add that I'm in favor of following the threading.py behavior of allowing <=0 to mean "non-blocking" (i.e., just check).  This would probably also benefit from a documentation update to clarify.