WebDevStudios/Custom-Metaboxes-and-Fields-for-WordPress — pull request #629 by nikolov-tmw (2014-07-24 00:52:19+00:00)
Title: Add support for meta diffs

Related issue - #588

I've added two more arrays that contain the old and new values for all fields saved from within the metabox.
This is especially useful if you need to create a diff between the two states of the post meta - for instance when you have to send an email with a summary of the changes.

@jtsternberg - looking forward to any comments/suggestions.