Fix image orientation for PIL engine

PIL lib ignored exif, when saving images.
Pillow lib has this behavior fixed, keeping exif is optional.
More info: https://github.com/python-imaging/Pillow/issues/183

After upgrade to Pillow, there was a regression, because sorl started
to save exif data while manually rotating images according exif.
It resulted in wrong thumbnail orientation.

This is now fixed by removing exif on save.
Merge pull request #224 from coagulant/fix-pil-orientation

Fix image orientation for PIL engine