Author selection becomes performance issue with large userbase with quick edit in admin

[wpmuguru]

MU Trac Ticket: ​http://trac.mu.wordpress.org/ticket/1086

When the author user base becomes too large, the script handling for the quick edit or inline edit begins to fail. In our specific situation, we have over 14000 authors for a single blog. This is causing the inline-edit-post.js to timeout and not completely render all the fields.

Since this would be such a rare issue, I think the best solution would be to just offer a hook that could keep the author option from being a part of the quick edit form. Since the field value is filled by js, then just replacing it with a hidden input keeps the author from being replaced on update.

probably dup of #5407