Feature notification after update should display only once

[tar.gz]

This is certainly an edge case, but still:

After an upgrade from 3.4 > 3.6, on a site where the post editor contains several metaboxes with file upload capacity, the user will see as many "New feature" notifications as there are metaboxes. Which can be quite a lot, in a WP-as-CMS-implementation.

I would assume that each "notification type" should be displayed only once, even if several similar metabox instances are present.

[nacin]

That's funky looking.

This is actually fairly easy to trigger in 3.6 due to the post locking pointer, if there are multiple posts being edited at the same time. This should be easy to fix, so moving to 3.6.1.

This should be simple to fix. Untested patch attached.

[helen]

#22735 was marked as a duplicate.

[SergeyBiryukov]

In 25117:

Avoid displaying multiple instances of the same feature pointers on a single screen. props nacin. fixes #25022 for trunk.

[SergeyBiryukov]

In 25118:

Avoid displaying multiple instances of the same feature pointers on a single screen. props nacin. fixes #25022 for 3.6.