jruby-1.6.3 Digest#file bug when run with JRUBY_OPTS=--1.9

gistfile1.rb

require 'pathname'
require 'digest'

`touch foo.txt`

path = Pathname.new 'foo.txt'
digest = Digest::MD5.new # digest type doesn't matter, see same problem with SHA1

# digest.file path  # this line throws an error when have JRUBY_OPTS=--1.9

# workaround 1:
digest.file path.to_s

# workaround 2:
class Digest::Base
  alias real_file file
  def file(something); real_file(something.to_s); end
end