Removal of object references

Signed-off-by: Timothy Warren <tim@timshomepage.net>

PHP5 returns object references by default, as such, the references used on objects all over CodeIgniter are redundant.

Simple test case to prove the default reference:

    class foo {
    var $blah = 5;
    }

    $foo = new foo();
    $bar = $foo;

    $foo->blah = 6;
    $bar->blah = 7;
    echo $foo->blah."<br />";
    echo $bar->blah."<br />";

This is, so far, just based on the core folder.