_edit_lock timestamp does not update on autosave() of non-changed, non-draft posts

[benbalter]

Admin_ajax does not properly update the _edit_lock timestamp in posts when:

1. The post->post_status != draft, and
2. The content of the post has not changed since the last autosave ping

STR:

1. Open up a post, page, or CPT that's either private or published
2. (wait 2 minutes or 2x your autosave ping, don't make any changes to the content)
3. Log in as another user and navigate to the post
4. User # 2 now has the file lock because User # 1's timestamp has expired

The Problem:

Lines 282 - 283 of autosave.dev.js (trunk) only POSTs auto_draft if it is "1".

Lines 985 - 992 expect non-auto_draft autosaves to post auto_draft as != 1.

Possibly Helpful for Background: r12991

So three possible scenarios:

1. Initial autodraft, auto_draft is posted as 1, line 992 updates _edit_post
2. Post content has changed, it's a true autosave, so _edit_lock gets update through edit_post()
3. Post content has not changed, it's not an autodraft, so auto_draft is not POSTed, and the lock is never updated.

Auto_draft will always either be 1 (and thus ID ='s 0) or not POST'd at all. Admin Ajax erroneously assumes it will be posted as != 1 when not an autodraft.

Proposed Fix:

If auto_draft is not set, update post lock. (patch attached).

Alternatively, could patch autosave.js to pass auto_draft of 1 on every non-auto_draft call.

(tested against trunk)

proposed non-autosave edit_lock patch