Improve auto_purge_post_terms_cache() post status handling.

Only purges post terms cache when post status is Publish or Private, or
when transitioning from Publish or Private post status to Draft,
Future, or Private.

See WebSharks/quick-cache#171
Merge branch 'refs/heads/140520-RC' into b-quick-cache-171
Auto-Purge properly when moving a post to the trash.

See WebSharks/quick-cache#171
Merge branch 'b-quick-cache-171' into 140520-RC