Create / Edit node and continue editing on same page after submit
The Save &amp; Edit module is a very basic module. It comprises of 6 total functions, so a port could be done less than a day. 

Alternatively, if the your requirement is to just save editing progress while keeping the editor window up, the Autosave form module does that. 

If you're looking to go the custom code route, some simple jQuery form manipulation can add a button which can trigger a form redirection &amp; submit. For example:

// Set the form destination to the edit form and submit it.
jQuery('form.node-form').attr('action', '/node/&lt;NID&gt;/edit?destination=node/&lt;NID&gt;/edit'); 
jQuery('.node-form').submit();