Description:
------------
One cannot create an object of the ReflectionFunction class for a function that has been disabled via the disable_functions configuration directive.

This effectively renders the ReflectionFunction::isDisabled() method useless.

Reproduce code:
---------------
--TEST--
ReflectionFunction::isDisabled()
--INI--
disable_functions=eval
--FILE--
<?php
$function = new ReflectionFunction('sort');
var_dump($function->isDisabled());

$function = new ReflectionFunction('eval');
var_dump($function->isDisabled());
?>
--EXPECT--
bool(false)
bool(true)


Expected result:
----------------
Test passes.

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

Fatal error: Uncaught exception 'ReflectionException' with message 'Function eval() does not exist' in /home/sb/ReflectionFunction_isDisabled.php:5
Stack trace:
#0 /home/sb/ReflectionFunction_isDisabled.php(5): ReflectionFunction->__construct('eval')
#1 {main}
  thrown in /home/sb/ReflectionFunction_isDisabled.php on line 5