FEATURE: add support for SIGTSTP which stops sidekiqs

Out of the box this signal "suspends" the process, but
we already use usr1 and usr2 and this is for an edge case
where the end user suspends it by typing "stop"

config/unicorn.conf.rb

@@ -77,6 +77,11 @@ before_fork do |server, worker|
 
       Demon::Sidekiq.start(sidekiqs)
 
+      Signal.trap("SIGTSTP") do
+        STDERR.puts "#{Time.now}: Issuing stop to sidekiq"
+        Demon::Sidekiq.stop
+      end
+
       class ::Unicorn::HttpServer
         alias :master_sleep_orig :master_sleep