Autosave causes problems if it never receives a response

[mdawaffe]

Since autosave disables the submit buttons, you can't save your data if it never gets a response from the server.

The button disabling was done to prevent collisions (multiple posts being created with same data), so we need a new way of preventing collisions.

Attached:

1. Re-enables buttons 1 second after disabling them.
2. Keeps a record of the last 24 hours worth of post_IDs (and what temporary negative number from which they initially came).
3. If you try to (auto)save a post with a negative post_ID, it first checks that record to see if that post has already been (auto)saved. If so, save that post under the real id.
4. Autosave will silently forgo writing to the DB if the post was saved less than autosave_interval / 2 = 120 / 2 = 60 seconds ago.

This is accomplished by:

1. new option: autosave_draft_ids
2. a hack each in wp_write_post() and edit_post() (the functions defined in admin-functions.php).

Collisions are still *possible*, but much less likely.

[ryan]

If two people are editing concurrently on the same blog, will there be contention when updating the autosave record? That's probably too corner-case to worry much about though.

[mdawaffe]

rboren: Just wondering if one might stomp the others changes to the array.
rboren: If they both get the array before the other writes.
mdawaffe: rboren: oh I see - yes that's possible
mdawaffe: I guess it could go in usermeta instead
rboren: Yeah, that's what I'm thinking.  Each user has his own autosave list.
mdawaffe: metakey = table_prefix . 'autosave_draft_ids'

[ryan]

Updated to use usermeta

[ryan]

(In [4760]) Autosave fixes from mdawaffe. fixes #3601