* array.c (rb_ary_tmp_new): added.
  This function creates internal use only array (which is completely
  hided by ObjectSpace.each_object) with filling nil.
  Otherwise, it can be incldues strange VALUEs.
* internal.h: added.
* node.h: use rb_ary_tmp_new_fill() for MEMO.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47189 b2dd03c8-39d4-4d8f-98ff-823fe69b080e