Remove old metadata when installing with --force.

Library/Homebrew/cask/lib/hbc/cask.rb

@@ -32,7 +32,6 @@ module Hbc
     end
 
     def metadata_path(timestamp = :latest, create = false)
-      return nil unless metadata_versioned_container_path.respond_to?(:join)
       if create && timestamp == :latest
         raise CaskError, "Cannot create metadata path when timestamp is :latest"
       end

Library/Homebrew/cask/lib/hbc/installer.rb

@@ -295,16 +295,15 @@ module Hbc
     end
 
     def save_caskfile
-      timestamp = :now
-      create    = true
-      savedir   = @cask.metadata_subdir("Casks", timestamp, create)
-      if Dir.entries(savedir).size > 2
-        # should not happen
-        raise CaskAlreadyInstalledError, @cask unless force
-        savedir.rmtree
-        FileUtils.mkdir_p savedir
+      unless (old_savedirs = Pathname.glob(@cask.metadata_path("*"))).empty?
+        old_savedirs.each(&:rmtree)
       end
-      FileUtils.copy(@cask.sourcefile_path, savedir) if @cask.sourcefile_path
+
+      return unless @cask.sourcefile_path
+
+      savedir = @cask.metadata_subdir("Casks", :now, true)
+      savedir.mkpath
+      FileUtils.copy @cask.sourcefile_path, savedir
     end
 
     def uninstall