Description:
------------
The order of the same priority is disordered

Test script:
---------------
$l = new \SplPriorityQueue;
$l->insert('e', 1);
$l->insert('a', 0);
$l->insert('b', 0);
$l->insert('c', 0);
$l->insert('d', 100);
var_dump($l);

Expected result:
----------------
d
e
a
b
c

Actual result:
--------------
object(SplPriorityQueue)#4 (3) {              
  ["flags":"SplPriorityQueue":private]=>      
  int(1)                                      
  ["isCorrupted":"SplPriorityQueue":private]=>
  bool(false)                                 
  ["heap":"SplPriorityQueue":private]=>       
  array(5) {                                  
    [0]=>                                     
    array(2) {                                
      ["data"]=>                              
      string(1) "d"                           
      ["priority"]=>                          
      int(100)                                
    }                                         
    [1]=>                                     
    array(2) {                                
      ["data"]=>                              
      string(1) "e"                           
      ["priority"]=>                          
      int(1)                                  
    }                                         
    [2]=>                                     
    array(2) {                                
      ["data"]=>                              
      string(1) "b"                           
      ["priority"]=>                          
      int(0)                                  
    }                                         
    [3]=>                                     
    array(2) {                                
      ["data"]=>                              
      string(1) "c"                           
      ["priority"]=>                          
      int(0)                                  
    }                                         
    [4]=>                                     
    array(2) {                                
      ["data"]=>                              
      string(1) "a"                           
      ["priority"]=>                          
      int(0)                                  
    }                                         
  }                                           
}