* enum.c: Enumerable#slice_after implemented.

* enumerator.c: Enumerator::Lazy#slice_after implemented.

  Requested by Tsuyoshi Sawada.  [ruby-core:58123] [Feature #9071]



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45981 b2dd03c8-39d4-4d8f-98ff-823fe69b080e