Follow r56795.  Since Ruby 2.2, calling #close on a closed
socket no longer raises exceptions.

* lib/cgi/session.rb (update): remove closed? check
* lib/net/http.rb (finish, transport_request): ditto
* lib/net/imap.rb (disconnect): ditto
* lib/net/pop.rb (do_start, do_finish): ditto
* lib/net/smtp.rb (do_start, do_finish): ditto
* lib/open3.rb (popen_run, pipeline_run): ditto
* lib/pstore.rb (transaction): ditto
* lib/shell/process-controller.rb (sfork):
* lib/tempfile (_close, call, Tempfile.create): ditto
* lib/webrick/httpauth/htdigest.rb (flush): ditto
* lib/webrick/httpauth/htpasswd.rb (flush): ditto
* lib/webrick/server.rb (start_thread, cleanup_shutdown_pipe): ditto

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@56865 b2dd03c8-39d4-4d8f-98ff-823fe69b080e