spec_for_dependency

# File lib/bundler/spec_set.rb, line 172
    def spec_for_dependency(dep, match_current_platform)
      specs_for_platforms = lookup[dep.name]
      if match_current_platform
        Bundler.rubygems.platforms.reverse_each do |pl|
          match = GemHelpers.select_best_platform_match(specs_for_platforms, pl)
          return match if match
        end
        nil
      else
        GemHelpers.select_best_platform_match(specs_for_platforms, dep.__platform)
      end
    end