fix(#144): ensure enum-types have unique names

[leberknecht]

When the column is of type Enum, we have to change the name, as enum types are per-database and not per-table, so creating a new enum with the same name will run into a conflict. closes #144

[coveralls]

Pull Request Test Coverage Report for Build 10720239536

Details

• 15 of 15 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 93.8%

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Totals
Change from base Build 7974435756:	0.02%
Covered Lines:	4921
Relevant Lines:	5177

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💛 - Coveralls