Ruby » Ruby master

• array.c (rb_ary_dup): reverted r39004. see [Bug #7768], and the
  release manager finailly decided to revert it.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39157 b2dd03c8-39d4-4d8f-98ff-823fe69b080e