Figure out why overwriting protection doesn't work.

[DarkDimius]

I recall dotty having protection from overwriting a user-defined class with a synthetic class with the same name by name-mangling sythetic one:
#313 (comment)

#2673 (comment) reports that it doesn't work in some cases.

[smarter]

The check should at least compare the names after normalizing the case.

[odersky]

The check should at least compare the names after normalizing the case.

That looks like a good plan.