Code review comment for lp:~allenap/launchpad/twisted-threading-bug-491870

Thanks for this improvement!

We talked about some things on IRC:
- Use of lambda is against LP coding style but common in Twisted. We will raise the issue at the reviewers meeting and you can leave it as it is for now. If the style change gets rejected, I ask you to fix this in a follow-up branch. Or wait until after the meeting before landing.
- The intended use of install_signal_handlers to avoid errors in the test should be documented.
- You agreed to add an explicit test for SerialScheduler.

Thanks for your patience with me ... ;-)