Upgrade add_permastruct() to allow more control over...

Upgrade add_permastruct() to allow more control over WP_Rewrite::generate_rewrite_rules(). See #16092.

The third argument is now a configuration array that mirrors the parameters of generate_rewrite_rules()
and allows for add_permastruct() specific args (i.e. with_front). The full configuration is stored in
WP_Rewrite::$extra_permastructs to be used by WP_Rewrite::rewrite_rules().


git-svn-id: https://core.svn.wordpress.org/trunk@19743 1a063a9b-81f0-0310-95a4-ce76da25c4cd