lastObject should not raise exceptions on empty arrayControllers

It fix an error introduced in c97a01947ea05654121cc8211908375637e4a7ac
Merge pull request #2142 from tchak/array-controller-fix

failing test with default arrayController content
Fix two linkTo unit tests that fail in IE9.  Tests used an <a> tag inside of a <button> tag, which IE9 does not like but works in other browsers.  Example: http://jsbin.com/ozemig/1/edit
Merge pull request #2145 from craigteegarden/ie9-linkTo-test-fix

Fix two linkTo unit tests that fail in IE9.  Tests used an <a> tag insid...