* enumerator.c (enumerator_with_index_i): add the declaration of
  rb_int_succ().  this fixes test failure on OS X introduced at r44745.


git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/branches/ruby_1_9_3@44748 b2dd03c8-39d4-4d8f-98ff-823fe69b080e