Function `set.distinct()` now supports optional comparable getter param.

[coveralls]

Pull Request Test Coverage Report for Build 4730409708

• 21 of 21 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 4707055179:	0.0%
Covered Lines:	1274
Relevant Lines:	1274

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💛 - Coveralls