def archive_tar_gz(treeish = 'master', prefix = nil)
      options = {}
      options[:prefix] = prefix if prefix
      self.git.archive(options, treeish, "| gzip -n")
    end
def archive_tar_gz(treeish = 'master', prefix = nil)
      options = {}
      options[:prefix] = prefix if prefix
      self.git.archive(options, treeish, "| gzip -n")
    end
Archive and gzip the given treeish
   +treeish+ is the treeish name/id (default 'master')
   +prefix+ is the optional prefix

 Examples
   repo.archive_tar_gz
   # => <String containing tar.gz archive>

   repo.archive_tar_gz('a87ff14')
   # => <String containing tar.gz archive for commit a87ff14>

   repo.archive_tar_gz('master', 'myproject/')
   # => <String containing tar.gz archive and prefixed with 'myproject/'>

 Returns String (containing tar.gz archive)