Add filter to _wp_post_revision_meta_keys() so developers can store custom meta data revisions

[c3mdigital]

In r23928 we added functionality to:

• Store the post format as meta on revisions (including autosaves).
• Add post formats data (post meta) when autosaving.

There is still no way to autosave and revision custom post meta.
Adding a filter to _wp_post_revision_meta_keys() will allow developers and plugin authors to effectively save post_meta revisions.

Related #20564,

[ocean90]

Also mentioned here ticket:20299:34.

[johnbillion]

It's worth noting that MarkJaquith's plan is to explicitly only store revisions for post format metadata in 3.6 and introduce an API for revisioning custom metadata at a later date.

[c3mdigital]

This should be closed since #20564 has been re opened this is a duplicate.