* struct.c (rb_struct_each_pair): use rb_yield_values(2, key, value)
  instead of rb_yield(rb_assoc_new(key, value)) if rb_block_arity()
  is greater than 1.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41986 b2dd03c8-39d4-4d8f-98ff-823fe69b080e