refactor image comparison

 - refactor NamedTemporaryFile to class instead of function factory
 - sublass it to ImageComparison
   - use with statement for cleaning up and optionally keeping testrun
     images
   - cleaner, shorter use in tests for image comparison
   - less duplicated code
image comparison: add option to obspy-runtests
try/except locale setting (for windows :P) and check backend
image comparison: check if failed-diff image exists before trying to
remove it
travis: upload images to imgur after test failure (thanks to @krischer :))
image comparison test setup tweaking
try to fix travis.yml
travis: keep images after testrun
fix image comparison test setup
try/except setting text.hinting_factor in image comparison setup
travis: try to fix image upload
use matplotlib 1.3 in travis
update baseline images to mapltotlib 1.3.0
update some more test baseline images
update some more test baseline images
update some more test baseline images
image comparison class: close image after testing (avoids warning about
many open figures from matplotlib)
image testing: set higher tolerance (matplotlib uses even higher value
of 13)
Merge remote-tracking branch 'upstream/master' into image_comparison

Conflicts:
	obspy/core/util/base.py
add missing import