Should autoLink escape ampersands?

Text::autoLink appears to escape ampersands in URLs. (Added to test case to demonstrate).

```
1) TextHelperTest::testAutoLink
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'This is a test text with URL <a href="http://www.cakephp.org?product_id=666&foo=bar&something=breaking" class="link" id="MyLink">http://www.cakephp.org?product_id=666&foo=bar&something=breaking</a>'
+'This is a test text with URL <a href="http://www.cakephp.org" class="link" id="MyLink">http://www.cakephp.org</a>?product_id=666&amp;foo=bar&amp;something=breaking'

/Users/robmcvey/Projects/cakephp/lib/Cake/Test/Case/View/Helper/TextHelperTest.php:154
```

If a URL has GET params, should autoLink remove these? The anchor text of the link will display as "&amp;" and the URL itself won't won't.
    
Happy to fix, or if this is indeed the desired behaviour (for a reason I can't think of!) please close.

Keep up the good work, fellas!