event_base_active_by_fd
Refactor evmap_{io,signal}_active_() to tolerate bad inputs
Merge remote-tracking branch 'ghazel/event_base_active_by_fd'
Sanity-check arguments to event_base_active_by_fd()
Add event_base_active_by_signal by analogy
Unit tests for active_by_fd; unsupport active_by_fd(TIMEOUT)

[It turns out that event_base_active_by_fd(TIMEOUT) didn't actually
work right. Feel free to add it back in as a patch.]