When tests fail, their stdout and stderr is printed as part of the summary, but
this helps suppress failure messages from #[should_fail] tests and generally
clean up the output of the test runner.
* All I/O now returns IoResult<T> = Result<T, IoError>
* All formatting traits now return fmt::Result = IoResult<()>
* The if_ok!() macro was added to libstd
I found awkward to have `MutableCloneableVector` and `CloneableIterator` on the one hand, and `CopyableVector` etc. on the other hand.
The concerned traits are:
* `CopyableVector` --> `CloneableVector`
* `OwnedCopyableVector` --> `OwnedCloneableVector`
* `ImmutableCopyableVector` --> `ImmutableCloneableVector`
* `CopyableTuple` --> `CloneableTuple`
