Close some figures when tests complete.

Unclosed figures cause warnings on subsequent tests.
Merge pull request #494 from QuLogic/close-test-figures

Close some figures when tests complete.
Merge pull request #493 from QuLogic/pillow

Make Pillow the only supported imaging library.
add python 3.4 to travis
try removing version restrictions from conda install because they aren't being found for python 3
install owslib only on python 2 for now (this will intentionally leads to errors on python 3)
move pep8 from conda to pip section
move several pure-python packages to pip install
Fix Travis' after_failure script with Python3.
Re-pin matplotlib version.
Test Python 3.3 too.
Make OWSLib optional.

The ImportError is deferred until the classes are actually used.
Skip OWSLib tests on Py3.