Merge pull request #6698 from MikeMcQuaid/upgrade-dependents-performance

Library/Homebrew/cmd/deps.rb

Library/Homebrew/cmd/upgrade.rb

Library/Homebrew/cmd/uses.rb

Library/Homebrew/dev-cmd/bottle.rb

Library/Homebrew/formula.rb

Library/Homebrew/formula_installer.rb

Library/Homebrew/formulary.rb

Library/Homebrew/keg.rb

Library/Homebrew/test/dependency_collector_spec.rb

Library/Homebrew/test/missing_formula_spec.rb

Library/Homebrew/test/os/linux/dependency_collector_spec.rb

Library/Homebrew/test/os/mac/dependency_collector_spec.rb

Library/Homebrew/test/spec_helper.rb

Library/Homebrew/test/tap_spec.rb