Mark timeout test (~20s) as slow.

[Carreau]

Make it skipped by default which highly reduce the runtime of the all test suite, at least locally when "just" running py.test.

[codecov]

Codecov Report

Merging #188 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
+ Coverage   98.44%   98.45%   +<.01%     
==========================================
  Files          53       53              
  Lines        6129     6131       +2     
  Branches      476      476              
==========================================
+ Hits         6034     6036       +2     
  Misses         80       80              
  Partials       15       15

Impacted Files	Coverage Δ
trio/tests/test_socket.py	100% <100%> (ø)	⬆️

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[njsmith]

Doh, sorry you hit this. This test is actually supposed to run quickly – I run the tests locally all the time, and get grumpy when they take more than ~2.5 seconds total. But I do this on Linux, and it turns out that this test is hitting a MacOS bug :-(. I happened to notice a little while ago while tracking down some other MacOS thing, and fixed it here: 8d40410
but unfortunately I was sloppy and so that fix is caught up in the giant branch of #107

[Carreau]

No worries, I can easily fix that locally. And yes sometime MacOs is a mess. I'm worried about APFS that will roll as a standard and unlike HFS+ stops normalizing unicode filenames.

[njsmith]

#107 is merged, so I think this should be fixed. (Please open an issue if not!)