Description:
------------
If you declare a closure as a static member of a class, you cannot call it directly.

Test script:
---------------
class T {
  public static $f;
}

T::$f = function() { echo "static member\n"; };
$f = function() { echo "local variable\n"; };

$f();
T::$f();

Expected result:
----------------
local variable
static member

Actual result:
--------------
local variable
Fatal error: Uncaught Error: Function name must be a string