Check for duplicates Fix

[minkvsky]

Fixes #467
I found the problem is caused while generating child_columns in es.get_pandas_data_slice;
I think a suitable solution is to adjust the vtypes of variable in relationship; On the other hand, now that we could change relationship.child_variable.id and relationship.parent_variable.id(es.add_relationship) in special case, we also standardize them as vtypes.Id or vtypes.Index

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #479 into master will decrease coverage by 0.02%.
The diff coverage is 96.49%.

@@            Coverage Diff             @@
##           master     #479      +/-   ##
==========================================
- Coverage   96.25%   96.23%   -0.03%     
==========================================
  Files         102      104       +2     
  Lines        8607     8658      +51     
==========================================
+ Hits         8285     8332      +47     
- Misses        322      326       +4

Impacted Files	Coverage Δ
featuretools/tests/testing_utils/mock_ds.py	87.85% <ø> (ø)	⬆️
...retools/primitives/standard/transform_primitive.py	100% <ø> (ø)	⬆️
...etools/primitives/base/transform_primitive_base.py	100% <100%> (ø)	⬆️
featuretools/entityset/entityset.py	95.04% <100%> (ø)	⬆️
...ools/primitives/base/aggregation_primitive_base.py	100% <100%> (ø)	⬆️
.../tests/primitive_tests/test_make_agg_primitives.py	100% <100%> (ø)
...ests/primitive_tests/test_make_trans_primitives.py	84.61% <84.61%> (ø)
...computational_backends/calculate_feature_matrix.py	96.98% <0%> (-0.87%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update cf98910...edcf04e. Read the comment docs.

[kmax12]

hi @minkvsky this looks great. thank you for tracking it down.

before we can merge, can you add a test case to make sure the variable type conversion during add relationships happens correctly?

[kmax12]

Looks good to me. Thank you!