added check for python-pillow PIL fork, in case python-imaging isn't found

Python Pillow is a fork of the inactive Python Imaging Library, which Arch Linux recently adopted as their python2-imaging replacement. 
Since Pillow doesn't use the global namespace, I added and extra check for Pillow in case importing 'Image' fails.
Add additional check for Pillow fork
Merge pull request #22 from ToostInc/pillow

Added an additional check for PIL, in case the Pillow fork is installed.