[4.6] Backport unwrapper PR

[Zac-HD]

Following up #5404.

[blueyed]

Fails on py27:

E AttributeError: 'module' object has no attribute 'unwrap'

[codecov]

Codecov Report

Merging #5453 into 4.6-maintenance will increase coverage by 0.27%.
The diff coverage is 100%.

@@                 Coverage Diff                 @@
##           4.6-maintenance    #5453      +/-   ##
===================================================
+ Coverage            95.91%   96.18%   +0.27%     
===================================================
  Files                  115      115              
  Lines                26407    26429      +22     
  Branches              2609     2610       +1     
===================================================
+ Hits                 25328    25421      +93     
+ Misses                 755      703      -52     
+ Partials               324      305      -19

Impacted Files	Coverage Δ
testing/test_doctest.py	100% <100%> (ø)	⬆️
src/_pytest/doctest.py	96.85% <100%> (+0.42%)	⬆️
src/_pytest/fixtures.py	97.55% <0%> (+0.27%)	⬆️
testing/test_capture.py	99.25% <0%> (+0.29%)	⬆️
testing/test_terminal.py	99.84% <0%> (+0.31%)	⬆️
testing/test_config.py	99.83% <0%> (+0.33%)	⬆️
testing/test_pdb.py	99.22% <0%> (+0.38%)	⬆️
src/_pytest/pytester.py	91.66% <0%> (+0.42%)	⬆️
src/_pytest/assertion/rewrite.py	95.77% <0%> (+0.48%)	⬆️
testing/python/fixtures.py	99.09% <0%> (+0.56%)	⬆️
... and 11 more

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