replace PIL with Pillow
Pillow: re-resolve #9864
doc: remove now unused environment variables
Pillow: fix patch to work against 2.2.2
remove PIL (it has been replaced by Pillow)
Pillow -> pillow
Trac #15539: use Pillow instead of PIL

PIL is has not been maintained an a few years. Pillow is the canonical
fork of PIL that most distributions have switch to using, we should do
the same.

Upstream Tarball: [[https://github.com/python-
imaging/Pillow/archive/2.2.2.tar.gz|Pillow-2.2.2.tar.gz]]

URL: http://trac.sagemath.org/15539
Reported by: ohanar
Ticket author(s): R. Andrew Ohana
Reviewer(s): François Bissey