Ticket #15819: capabilities.php.diff

Index: capabilities.php
===================================================================
--- capabilities.php    (revision 23176)
+++ capabilities.php    (working copy)
@@ -1365,6 +1365,37 @@
 }
 
 /**
+ * Whether a particular user has capability or role.
+ *
+ * @since 3.5.1
+ *
+ * @param int|object $user User ID or object.
+ * @param int $blog_id Blog ID
+ * @param string $capability Capability or role name.
+ * @return bool
+ */
+function user_can_for_blog( $user, $blog_id, $capability ) {
+       if ( is_multisite() )
+               switch_to_blog( $blog_id );
+               
+       if ( ! is_object( $user ) )
+               $user = get_userdata( $user );
+
+       if ( ! $user || ! $user->exists() )
+               return false;
+
+       $args = array_slice( func_get_args(), 3 );
+       $args = array_merge( array( $capability ), $args );
+
+       $can = call_user_func_array( array( $user, 'has_cap' ), $args );
+
+       if ( is_multisite() )
+               restore_current_blog();
+               
+       return $can;    
+}
+
+/**
  * Retrieve role object.
  *
  * @see WP_Roles::get_role() Uses method to retrieve role object.