brew-unpack: don't chdir further than a normal install would

If we want to generate usable patches from inside the unpacked source,
then we should start from the same directory that a normal install
would start from.

Library/Contributions/cmd/brew-unpack.rb

@@ -81,11 +81,7 @@ module Homebrew extend self
 
       oh1 "Unpacking #{f.name} to: #{stage_dir}"
       ENV['VERBOSE'] = '1' # show messages about tar
-      f.brew do
-        entries = Dir['*']
-        cd entries.first if entries.length == 1 && File.directory?(entries.first)
-        cp_r getwd, stage_dir
-      end
+      f.brew { cp_r getwd, stage_dir }
       ENV['VERBOSE'] = nil
 
       if ARGV.switch? 'g'