Add 'ep_mask' as an argument to the 'rewrite' array for register_post_type()...

Add 'ep_mask' as an argument to the 'rewrite' array for register_post_type() and register_taxonomy(). Keeps 'permalink_epmask' compatible as an argument for post type registrations. Fixes endpoints for category and tag pages. fixes #19275.

git-svn-id: https://core.svn.wordpress.org/trunk@19738 1a063a9b-81f0-0310-95a4-ce76da25c4cd