Make global subscribe more reliable
Make global subscribe more reliable

FIX: on reconnect we were not catching up on messages
FEATURE: add keepalive that ensure subscribe thread can
  process messages

jemminger/message_bus,menxu/message_bus,nathanstitt/message_bus,SamSaffron/message_bus,SamSaffron/message_bus,nathanstitt/message_bus,cannikin/message_bus,MadBomber/message_bus,riking/message_bus,MadBomber/message_bus,wlads/message_bus,wlads/message_bus,cannikin/message_bus,nathanstitt/message_bus,MadBomber/message_bus,jemminger/message_bus,wlads/message_bus,riking/message_bus,cannikin/message_bus,menxu/message_bus,jemminger/message_bus