Fix ValueError: invalid PNG header on Windows

[cgohlke]

On Windows the urlparse(...).scheme != '' test for URLs does not work.
For file names the drive letter is returned as scheme.

See also #5071.

This fixes one test failure on Windows:

======================================================================
ERROR: matplotlib.tests.test_image.test_imread_pil_uint16
----------------------------------------------------------------------
Traceback (most recent call last):
  File "X:\Python34\lib\site-packages\nose\case.py", line 198, in runTest
    self.test(*self.arg)
  File "X:\Python34\lib\site-packages\matplotlib\testing\decorators.py", line 53, in failer
    result = f(*args, **kwargs)
  File "X:\Python34\lib\site-packages\matplotlib\tests\test_image.py", line 95, in test_imread_pil_uint16
    'baseline_images', 'test_image', 'uint16.tif'))
  File "X:\Python34\lib\site-packages\matplotlib\pyplot.py", line 2290, in imread
    return _imread(*args, **kwargs)
  File "X:\Python34\lib\site-packages\matplotlib\image.py", line 1324, in imread
    return handler(fd)
ValueError: invalid PNG header

[tacaswell]

@WeatherGod please backport

[WeatherGod]

Ok, I think I did it right:

[centos6] [broot@rd22 matplotlib]$ git cherry-pick 3e28138
Finished one cherry-pick.
[v1.5.x 6107fb5] Fix ValueError: invalid PNG header on Windows
 Author: Christoph Gohlke <cgohlke@uci.edu>
 1 files changed, 1 insertions(+), 1 deletions(-)
[centos6] [broot@rd22 matplotlib]$ git push origin v1.5.x 
Counting objects: 9, done.
Delta compression using up to 8 threads.
Compressing objects: 100% (4/4), done.
Writing objects: 100% (5/5), 2.72 KiB, done.
Total 5 (delta 2), reused 3 (delta 1)
To git@github.com:matplotlib/matplotlib
   c8eea31..6107fb5  v1.5.x -> v1.5.x

[tacaswell]

I usually cherry-pick the merge commit, git cherry-pick -m 1 c01ed60 which will work if the PR has multiple commits.

[WeatherGod]

Ah, that's what I was doing wrong! I was referencing the PR's commit when I
tried it, not the merge commit. Ok, good to know going forward.

On Mon, Oct 5, 2015 at 3:05 PM, Thomas A Caswell notifications@github.com
wrote:

I usally cherry-pick the merge commit, git cherry-pick -m 1 c01ed60 which
will work if the PR has multiple commits.

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