Add tests for a few issues which can now be closed

[alexcrichton]

Closes #5844

[huonw]

There's already a test for the Unfoldr ICE. (I believe that issue is a duplicate, because I vaguely remember closing an issue when I fixed it.)

[alexcrichton]

Should both tests be included though? The issue mentioned that the error was an ICE, not a normal compiler error. Even with the run-pass test it's probably a good idea to ensure the compiler also doesn't horribly die when given invalid input.

[huonw]

Yeah, I fixed an ICE. (Obviously it's fine to have both... but the files are essentially the same, so it's possibly pointless.)

[alexcrichton]

Did the ICE happen when the code had the correct order of arguments for the issue? If so, then the cfail test is superfluous.

[huonw]

Oh! I misread the test; but the order of arguments was changed since that issue was filed (b9cf6a3) and so I think that wasn't the underlying problem.

[alexcrichton]

Updated to remove the redundant test.