Changes across branches fail to render data constructors

[rlmark]

There are a few cases where clicking "expand" on the Changes view of a term on Share directs the user to a "Page not found" separate page or produces an error instead of displaying the changes. Changing the data constructors of a type and filing a PR is one such case!

In an effort to help minimize the surface area of things, here's a project with a simple PR demonstrating the issue.

Notes:

• transitive changes appear to render as expected
• in this PR, it's just the data constructors that create the error, not other actual code changes.