Rainbows! 4.4.2 - EventMachine async.callback fix
One bugfix allows stream(:keep_open) in Sinatra to work
properly.
Thanks to W. Andrew Loe III for the informative bug report
and reproducible test case.
ref: http://mid.gmane.org/CA+-9oNd1EFqsniPkkPTwu5opTCinbM7-2KHoXov7+y3LE4s4Tg@mail.gmail.com