Merge remote-tracking branch 'upstream/master' into save-artifacts_sizes

* upstream/master: (175 commits)
  Document Repository#keep_around
  Don't garbage collect commits that have related DB records like comments
  Update CHANGELOG
  Update RedCloth to 4.3.2 for CVE-2012-6684
  Fix typo in Merge Requests API documentation
  Downgrade to Redis 3.2.2 due to massive memory leak with Sidekiq
  Enable Style/EmptyLines cop, remove redundant ones
  Update CHANGELOG
  Cache results from jQuery selectors to retrieve namespace name
  Fix import button when import fail due the namespace already been taken
  Fix snippets comments not displayed
  Fix emoji paths in relative root configurations
  Exclude requesters from Project#members, Group#members and User#members
  Upgrade Thin from 1.6.1 to 1.7.0.
  Many squashed commits
  Cache autocomplete results
  Upgrade Sidekiq from 4.1.2 to 4.1.4.
  Upgrade seed-fu from 2.3.5 to 2.3.6
  use has_many relationship with events
  Support creating a todo on issuables via API
  ...