Description:
------------
When calling is_callible on a public function inherited from a parent, it will 
return false.

Test script:
---------------
class a
{
    public function bla() {}
}

class b extends a
{
}

$b = new b;
var_dump(is_callable($b, 'bla'));


Expected result:
----------------
bool(true)

Actual result:
--------------
bool(false)