Report duplicated test names via printer

[auduchinok]

Fixes #336.

[haf]

Have you validated this on a terminal, so that it doesn't mess up e.g. the console/ANSI escape codes?

[auduchinok]

Nope, only run the test suite via fake.
Isn't it something that should be covered by the printers (already)?

[haf]

@auduchinok It is, but I never got around to proving that property in my head, because there's a certain amount of global state when printing (-ansi) to the console singleton. In all likelyhood, it's enough for you to run expecto with itself through its test suite on your terminal and see that it works.

[haf]

@auduchinok thank you for your contribution!