hook to the 'posts_selection' action to restore the $wp_query->is_author flag back to TRUE if we have a coauthors-plus taxonomy query.

see https://github.com/GigaOM/gigaom/issues/4904
use an object var to track the state of the author => taxonomy query conversion

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typo
Merge pull request #26 from wluo/github-4904

hook to the 'posts_selection' action to restore the $wp_query->is_author flag