brew fetch --force to force redownload of tarballs

External command "brew fetch" now allows -f|--force to remove an
existing cached file before downloading.

Library/Contributions/examples/brew-fetch.rb

@@ -1,7 +1,13 @@
 # Downloads the tarballs for the given formulae to the Cache
 
 require 'formula'
+require 'fileutils'
 
 ARGV.formulae.each do |f|
+  if ARGV.include? "--force" or ARGV.include? "-f"
+    where_to = `brew --cache #{f.name}`.strip
+    FileUtils.rm_rf where_to unless where_to.empty?
+  end
+
   f.downloader.fetch
 end