Automattic/Co-Authors-Plus — pull request #67 by ericmann (2012-10-25 23:07:08+00:00)
Title: Map author slugs to user_nicename

Entries in the author taxonomy were originally created using the user login. Without spaces, this was fine, but *with* spaces caused problems. The user with login "john doe" was mapped to the author term with the slug "john-doe" ... WordPress was unable to retrieve authors from the taxonomy if their login contained spaces.

This patch uses the `user_nicename` instead. Functionally, it is identical to the user login but, like the slugs in the author taxonomy, replaces spaces with hyphens. `get_term_by( 'slug', $found_user->user_nicename, $this->coauthor_taxonomy );` will return matches both for users with and without spaces in their login names.