Comment 10 for bug 908944

I've just been using the new version, and I realized that if you only have a single session, byobu-select-session doesn't call update_environment before attaching to it. This is because the attachment code is somewhat duplicated, and I only fixed one instance. I'm attaching a patch to fix this by eliminating the code duplication, causing all attachment to existing sessions to happen via the attach_session function.