Add signalfd_fixup and signal activation.
Actually ... remove the signalfd/sigprocmask stuff - don't complicate manhole with workarounds for the crappy linux signals/threads.
Remove poll_interval too ...
Add tests for activate_on and the signalfd signal delivery race-condition (between the manholethread and the mainthread).
Extend the race-condition test a bit.
Change to colored test output.
Update readme.