merge revision(s) 39650: [Backport #8043]

	* marshal.c (w_extended): check for prepended object.
	  [ruby-core:53206] [Bug #8043]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_0_0@40087 b2dd03c8-39d4-4d8f-98ff-823fe69b080e