Dont pickle abc caches of instances of abc.ABCMeta subclasses.

[pierreglaser]

Closes #302

Don't pickle the abc caches populated during isinstance/issubclass checks against instances of abc.ABCMeta subclasses.

[pierreglaser]

@llllllllll if you want to take a look.

[codecov]

Codecov Report

Merging #303 into master will decrease coverage by 13.97%.
The diff coverage is 88.23%.

@@             Coverage Diff             @@
##           master     #303       +/-   ##
===========================================
- Coverage   92.84%   78.86%   -13.98%     
===========================================
  Files           2        2               
  Lines         852      861        +9     
  Branches      177      178        +1     
===========================================
- Hits          791      679      -112     
- Misses         37      143      +106     
- Partials       24       39       +15

Impacted Files	Coverage Δ
cloudpickle/cloudpickle_fast.py	94.84% <87.5%> (-0.31%)	⬇️
cloudpickle/cloudpickle.py	72.92% <88.88%> (-19.08%)	⬇️

---

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[codecov]

Codecov Report

Merging #303 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #303   +/-   ##
======================================
  Coverage    92.9%   92.9%           
======================================
  Files           2       2           
  Lines         860     860           
  Branches      179     179           
======================================
  Hits          799     799           
  Misses         37      37           
  Partials       24      24

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[ogrisel]

LGTM. Maybe @pitrou wants to have a look as I think he originally contributed the 3.7+ code.

[ogrisel]

LGTM but the changelog need an update.