Work on 0.2.19pre.
Reduce wd options to `wd-url`.

Continue to parse old options for back-compat.
Send a bogus WebDriver command every 15s.

Keeps WebDriver from timing out due to no activity.
Bugfix: isExecuting is not a setter.
If we still have tests without results, resend.

If all tests have been given to browsers, but we are still
not complete, resend the pending tests to browsers that ask
for more tests until we get results for all tests.