Description:
------------
SplObjectStorage will be a lot more useful if I could override the hash function 
it uses, so different objects which are really equal will be recognized as such by 
SplObjectStorage.

While I currently do this by jumping through a few hoops, this will be a welcome 
addition. A __hashCode() magic method can accomplish this easily.

Test script:
---------------
Pseudo-code:
<?
class StockSecurity {
	public $exchange;
	public $ticker;
	
	public function __hashCode() {
		return $this->exchange . ":" . $this->ticker;
	}
}

$d = new SplObjectStorage();
$s = new StockSecurity( 'NASDAQ', 'GOOG' );
$d->attach( $s, getStockQuote( $s ) );

// later on, in a different method
$s = new StockSecurity( 'NASDAQ', 'GOOG' );
$quote = $d[ $s ];