* add TimerFD::CANCEL_ON_SET constant
ref: http://www.man7.org/tlpi/api_changes/
* fix concurrent Epoll#wait on the same epoll fd
* SignalFD interface removed (unworkable with Ruby runtimes)
* use rb_update_max_fd() if available (Ruby 1.9.3)
* reintroduce SLEEPY_PENGUIN_VERSION constant ("3.1.0")