Fix issue #8763

Issue #8763 is about improving a particular error message.

* added case & better error message for "impl trait for module"
* added compile-fail test trait-impl-for-module.rs
* updated copyright dates
* revised compile-fail test trait-or-new-type-instead
   (the error message for the modified test is still unclear, but that's a different bug https://github.com/mozilla/rust/issues/8767)