eval.c: copy special exception

	* eval.c (setup_exception): make unfrozen copy of special
	  exception before setting up a cause.
	test_io.rb: separate a test

	* test/ruby/test_io.rb (test_closed_stream_in_rescue): run in a
	  separated process.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@59538 b2dd03c8-39d4-4d8f-98ff-823fe69b080e