Update testcases.docopt

I'm not 100% sure that all my changes are correct (especially the first few to `"user-error"`, but I couldn't find anything in the Docopt README that said names can be accessed via prefix).

Would you be open to adding tests that require more sophisticated pattern matching? e.g., `cp FILE... DIR`. I have it working in my [Rust port](https://github.com/BurntSushi/docopt.rs) along with all tests passing.