Raise exceptions in consistency check

[therve]

isInconsistent can return a boolean, add a new wrapper which checks the
return type and use that instead.

Fixes #178

[codecov-io]

Codecov Report

Merging #188 into master will increase coverage by 0.16%.
The diff coverage is 82.35%.

@@            Coverage Diff             @@
##           master     #188      +/-   ##
==========================================
+ Coverage   85.49%   85.66%   +0.16%     
==========================================
  Files          26       26              
  Lines        4662     4654       -8     
==========================================
+ Hits         3986     3987       +1     
+ Misses        676      667       -9

Impacted Files	Coverage Δ
pyasn1/codec/ber/decoder.py	84.31% <100%> (+0.05%)	⬆️
pyasn1/codec/cer/encoder.py	86.52% <100%> (+0.51%)	⬆️
pyasn1/codec/ber/encoder.py	84.91% <100%> (+0.8%)	⬆️
pyasn1/codec/native/encoder.py	86.45% <50%> (+1.45%)	⬆️
pyasn1/type/univ.py	84.41% <75%> (+0.09%)	⬆️

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