add new ubuntu in deb build script
fix a test
fix image comparison for older matplotlib (see http://tests.obspy.org/10323/#1)
add option to skip flake8 test in obspy-runtests
handle skipping of image tests inside ImageComparison

- fixes http://tests.obspy.org/10359/#1
- removes code duplication
fix segy benchmark image test
Revert/adapt "handle skipping of image tests inside ImageComparison"

This reverts commit 78c57678e7b5fcf3ad837ad546498df1c3a14747 (plus some
further adaptions) because `unittest.SkipTest` is not available on
Python 2.6
if mpl < 1.2: check for PIL before trying to use mpl's compare_images
deb packages: add python-imaging to recommends

it enhances matplotlib (e.g. save to .jpg files) but has been added to
matplotlib's recommends only recently (see
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=725047)
make flake8 check reusable
refactor: move all routines related to testing from util.base to new util.testing
update make_pep8.py in docs (fixes #666 \m/)