Make bottle code cross-platform.

Library/Homebrew/bottles.rb

Library/Homebrew/cleanup.rb

Library/Homebrew/cmd/bottle.rb

Library/Homebrew/cmd/pull.rb

Library/Homebrew/cmd/test-bot.rb

Library/Homebrew/extend/os/bottles.rb

Library/Homebrew/extend/os/mac/utils/bottles.rb

Library/Homebrew/formula.rb

Library/Homebrew/formula_installer.rb

Library/Homebrew/formulary.rb

Library/Homebrew/software_spec.rb

Library/Homebrew/test/test_bottle_collector.rb

Library/Homebrew/test/test_bottle_tag.rb

Library/Homebrew/test/test_formulary.rb

Library/Homebrew/test/testball_bottle.rb

Library/Homebrew/utils/bottles.rb

Library/brew.sh