FIX #526: Do not depend on test-sources

[ankostis]

• Move HIDE_WINDOWS_KNOWN_ERRORS flag from
  git.test.lib.helper-->git.util;
  regular modules in main-sources folder also depend on that flag.
• Use unittest.SkipTest instead of from non-standard nose lib.

[ankostis]

It is strange...in my appveyor project, this PR pases OK: https://ci.appveyor.com/project/ankostis/gitpython/build/1.0.226

[edit] and it is a different commit, from a different branch! (master instead of nonose)

[codecov-io]

Current coverage is 93.66% (diff: 81.81%)

Merging #527 into master will increase coverage by 0.03%

@@             master       #527   diff @@
==========================================
  Files            63         63          
  Lines          9652       9651     -1   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits           9038       9040     +2   
+ Misses          614        611     -3   
  Partials          0          0          

Powered by Codecov. Last update 9557508...aafde7d

[ankostis]

There is something fishy going on...I just amended and re-pushed the commit, and still in the Appveyor I'm getting a commit-id that I do not have it in my local repo: cc096ddf

Clicking on to it I see that it is a merge commi, only present on GitHub - but this PR is not yet merged, and actually it is explicitly not based on the latest master, to avoid errors from #513. But this "automatic merge" behavior is defeating my goal.

@ Byron any idea why this is happening?

[Byron]

@ankostis I am looking into the appveyor settings right now - even though I didn't change them at all, maybe there is a checkbox to turn that behaviour off.

[ankostis]

I don't know either if this auto merge is configurable.
As long as there are no master failures, it won't be a problem B- so you can forget about it.

[Byron]

Alright - I also didn't find anything - apparently turning this behaviour off is not that easy.