Fix the X-UA-Compatible header for IE8, fixes #25575
Built from https://develop.svn.wordpress.org/trunk@26089


git-svn-id: http://core.svn.wordpress.org/trunk@26007 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix canonical redirection of `cat` as described in #15256 by rolling the `cat` query var into `tax_query`, instead of `category__in` / `category__not_in`. Top-level categories were only redirecting properly if they had no children.

All unit tests pass. Tests marked for #15256 are no longer skipped.

Fixes #15256.
Props dd32.


Built from https://develop.svn.wordpress.org/trunk@26090


git-svn-id: http://core.svn.wordpress.org/trunk@26008 1a063a9b-81f0-0310-95a4-ce76da25c4cd