"Bus error: 10" fix

The really serious bug fix in my pull request is: https://github.com/Kronuz/django-imagekit/commit/9ca5d7ea7713f7fa52db8ac0fbf80e11ef5a039e ...which made python crash with a "Bus error: 10" here.

The others are adding Watermark and a "Frame" processor as well as using RGBA for reflections and the faster cStringIO module.