Introduce wp_clean_themes_cache() for upgrades and testing. fixes #20954.

git-svn-id: https://develop.svn.wordpress.org/trunk@21080 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/theme.php

@@ -106,6 +106,18 @@ function wp_get_theme( $stylesheet = null, $theme_root = null ) {
 	return new WP_Theme( $stylesheet, $theme_root );
 }
 
+/**
+ * Clears the cache held by get_theme_roots() and WP_Theme.
+ *
+ * @since 3.5.0
+ */
+function wp_clean_themes_cache() {
+	delete_site_transient('update_themes');
+	search_theme_directories( true );
+	foreach ( wp_get_themes( array( 'errors' => null ) ) as $theme )
+		$theme->cache_delete();
+}
+
 /**
  * Whether a child theme is in use.
  *