zipped with nil if argument arrays are shorter.  if arrays are
  longer, left items are ignored.  now works with blocks.

* enum.c (zip_i): changed for new behavior.

* array.c (rb_ary_transpose): added. [new]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@3064 b2dd03c8-39d4-4d8f-98ff-823fe69b080e