Backed out changesets 1d9b6d754b9d and 73782d1e750c for landing with the wrong bug number.
Bug 1000695 - Part 1: Rewrite backgroundUpdateCheck() to Task.jsm based async. r=unfocused
Bug 1000695 - Part 2: Yield to event loop after receiving onInstallEnded, rewrite to Task.jsm. r=unfocused