Back compat for 5-year-old MU allowed_themes code
|Reported by:||nacin||Owned by:|
 removed get_site_allowed_themes() and wpmu_get_blog_allowedthemes().
Both of these functions used an option key called allowedthemes that stored an array of allowed themes, keyed by stylesheet and valued with (int) 1.
Five years ago, there was an option called allowed_themes, that stored an array of allowed themes, keyed by untranslated theme name (like get_themes()) and again valued with (int) 1.
For more on this, see http://mu.trac.wordpress.org/changeset/936 (and in general you can search "allowedthemes" or "allowed_themes" on mu.trac, for more changesets and tickets).
We should consider adding some light back compat code to WP_Theme to support the old option.