Description:
------------
When serializing an object that has a sleep method and this method returns a non-string value the value generated by serialize is corrupted and can't be unserialized.

It works fine with values that are strings but not attribute (see http://3v4l.org/Fprda), but it doesn't with non-string values (see http://3v4l.org/81nem or the test script below).

HHVM works fine with non-strings. I wrote a patch that makes the PHP to works the same way (patch attached and available on https://github.com/php/php-src/pull/1057).

Test script:
---------------
<?php

class C {
	public $a = true;

	public function __sleep() {
		return ['a', 1];
	}
}

$a = new C;

$s = serialize($a);
var_dump($s);
var_dump(unserialize($s));

Expected result:
----------------
Notice: serialize(): "1" returned as member variable from __sleep() but does not exist in /in/81nem on line 13
string(30) "O:1:"C":2:{s:1:"a";b:1;i:1;N;}"
object(C)#2 (2) {
  ["a"]=>
  bool(true)
  ["1"]=>
  NULL
}

Actual result:
--------------
Notice: serialize(): __sleep should return an array only containing the names of instance-variables to serialize. in /in/81nem on line 13
string(26) "O:1:"C":2:{s:1:"a";b:1;N;}"

Notice: unserialize(): Error at offset 25 of 26 bytes in /in/81nem on line 15
bool(false)