Fix the return value of get_theme_root() when the theme root is outside of...

Fix the return value of get_theme_root() when the theme root is outside of WP_CONTENT_DIR, thus making it absolute rather than the typical relative theme root.

Make get_theme_root_uri() tolerate an absolute path for a theme root. It will now make an attempt to find a corresponding URL for absolute paths as well.

see #17597.



git-svn-id: https://core.svn.wordpress.org/trunk@20016 1a063a9b-81f0-0310-95a4-ce76da25c4cd