* lib/tsort.rb: Returns an enumerator if no block is given.
  [ruby-core:66270] [Feature #10508] Proposed by Andrey Savchenko.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@48584 b2dd03c8-39d4-4d8f-98ff-823fe69b080e