Description:
------------
callable typehint and is_callable may return true for a string with double colon, but it's not callable with parentheses. On the page

http://php.net/manual/en/language.types.callable.php

"As of PHP 5.2.3, it is also possible to pass 'ClassName::methodName'"

Well, able to pass, but cannot use.

Occurs in PHP 5.6. PHP 7.0 doesn't have this problem, it works properly.

Test script:
---------------
<?php
namespace ns {
    class cls{
        static function sfn(){
            return 'OK';
        }
    }
}

namespace {
    function mycallfn(callable $x){
        if(is_callable($x)){
            return $x();
        }else{
            return 'FAIL';
        }
    }
    echo mycallfn(["ns\\cls", "sfn"])."\n";
    echo mycallfn("ns\\cls::sfn")."\n";
}


Expected result:
----------------
OK
OK


Actual result:
--------------
OK
PHP Fatal error:  Call to undefined function ns\cls::sfn() on line 13