Automattic/Co-Authors-Plus — pull request #200 by bcampeau (2014-05-03 23:33:23+00:00)
Title: Added filter for guest author linked account dropdown args

By default, the linked account dropdown will show all users, which is inefficient for a site with public user accounts since the vast majority of users would never be linked to a guest author. By adding a filter here, it creates the option to limit this to author users, such as by using the 'who' parameter.