Improve error message when a recursive dependency between fixtures is detected

[nicoddemus]

Fix #2909

[codecov]

Codecov Report

Merging #4207 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master   #4207      +/-   ##
=========================================
- Coverage   95.81%   95.8%   -0.01%     
=========================================
  Files         109     109              
  Lines       24257   24314      +57     
  Branches     2390    2405      +15     
=========================================
+ Hits        23242   23295      +53     
- Misses        720     722       +2     
- Partials      295     297       +2

Flag	Coverage Δ
#docs	28.51% <0%> (ø)	⬆️
#doctesting	28.51% <0%> (ø)	⬆️
#linting	28.51% <0%> (ø)	⬆️
#linux	95.58% <100%> (-0.01%)	⬇️
#nobyte	91.89% <100%> (+0.01%)	⬆️
#numpy	92.86% <100%> (-0.04%)	⬇️
#pexpect	41.26% <0%> (-0.01%)	⬇️
#py27	93.94% <100%> (ø)	⬆️
#py34	92.23% <100%> (+0.04%)	⬆️
#py35	92.24% <100%> (+0.04%)	⬆️
#py36	93.89% <100%> (-0.01%)	⬇️
#py37	92.26% <100%> (+0.03%)	⬆️
#trial	92.86% <100%> (-0.04%)	⬇️
#windows	94.05% <100%> (ø)	⬆️
#xdist	93.78% <100%> (+0.15%)	⬆️

Impacted Files	Coverage Δ
src/_pytest/fixtures.py	97.3% <100%> (ø)	⬆️
testing/python/fixture.py	99.24% <100%> (ø)	⬆️
src/_pytest/capture.py	93.36% <0%> (-0.46%)	⬇️
src/_pytest/logging.py	95.66% <0%> (-0.11%)	⬇️
testing/logging/test_reporting.py	100% <0%> (ø)	⬆️

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