Summary: Ref T8509. This fixes three issues: - Adding a slug like `UPPERCASE` would not give you a normalized slug. (Now: normalizes as `uppercase`.) - Adding a slug like `UPPERCASE` would allow you to give two different projects the different tags `UPPERCASE` and `uppercase` (and `UpPeRcAsE`, etc). (Now: second tag is rejected as a duplicate.) - Adding multiple identical or similar slugs would produce a duplicate key exception. (Now: ignores the duplicates.) Test Plan: - Added test coverage. - Made tests pass. - Hit these cases in the UI. Reviewers: chad Reviewed By: chad Maniphest Tasks: T8509 Differential Revision: https://secure.phabricator.com/D14870