fix bug 773054 - Allow S&CE on edits

https://bugzilla.mozilla.org/show_bug.cgi?id=773054

Since we no longer allow slug changes on the edit forms (doc and template), there's no reason to not allow Save And Continue Editing.  To test:

1.  Open a document in one tab, the rev dash in another
2.  In the JS Console, execute:  `jQuery("#id_current_rev").attr("value");`
3.  Make a change to the doc, click S&CE
4.  After the spinner is done, execute `jQuery("#id_current_rev").attr("value");` again and see the revision incremented
5.  Switch over to the rev dash tab and refresh;  see the new revision

Rinse and repeat.