Introduce is_ms_switched(). see #21459

git-svn-id: https://develop.svn.wordpress.org/trunk@21560 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/ms-blogs.php

@@ -567,6 +567,17 @@ function restore_current_blog() {
 	return true;
 }
 
+/**
+ * Determines if switch_to_blog() is in effect
+ *
+ * @since 3.5.0
+ *
+ * @return bool True if switched, false otherwise.
+ */
+function is_ms_switched() {
+	return $GLOBALS['_wp_switched'];
+}
+
 /**
  * Check if a particular blog is archived.
  *