Improved animated GIF support

I've been using Imagine in a special service we provide to our clients, which manipulates images on demand. I found out that animated GIFs did not work at all. Particularly slightly more complex GIFs that require coalescing wouldn't work at all.

The changes in this pull request are small and limited to Imagick. All tests pass and I added an extra animated GIF (courtesy of [Cyndi Norrie](http://cyndipop.tumblr.com/) via [15 Folds](http://15folds.com)) for testing purposes.

I took a quick peek at Gmagick too, but those tests failed for me regardless. That might be due to my build (MacPorts, php5x-gmagick=1.1.7RC2) but even more curiously the exception that gets thrown breaks the Imagick tests too. As I don't know Gmagick at all I didn't touch those files until I can get my installation working or someone else can test it.

There are no API changes, only difference is that animation delay is now null by default - which means it won't set a delay on the frames, keeping the delay from the original (if any) instead. While this may result in strange results when creating GIFs and not setting the delay, it will not break the output (nor is it a likely use case). This change would make sense for Gmagick too, but as I can't test it right now, I didn't want to potentially break it.