Description:
------------
SplPriorityQueue does not behave as expected when data is registered with equal 
priority. One would expect one of the following situations:

 * The data retain the same order as how they were registered
 * The data are ordered based on value

Neither of these are the case, however. From empirical analysis, it appears that 
the following happens:

 * The first item registered at that priority will always be the first returned
 * The remaining items are returned in the reverse order in which they were 
enqueued.

Test script:
---------------
$queue = new SplPriorityQueue();
$queue->insert('foo', 100);
$queue->insert('bar', 100);
$queue->insert('baz', 100);
$queue->insert('bat', 100);

foreach ($queue as $data) {
    echo $data, "\n";
}

Expected result:
----------------
// IDEALLY order in which they are registered:
foo
bar
baz
bat

// OR following same rules as priority queue -- higher values == higher priority
foo
baz
bat
bar



Actual result:
--------------
foo
bat
baz
bar