ui: restore behavior to ignore some I/O errors (issue5658) e9646ff34d55 and 1bfb9a63b98e refactored ui methods to no longer silently swallow some IOError instances. This is arguably the correct thing to do. However, it had the unfortunate side-effect of causing StdioError to bubble up to sensitive code like transaction aborts, leading to an uncaught exceptions and failures to e.g. roll back a transaction. This could occur when a remote HTTP or SSH client connection dropped. The new behavior is resulting in semi-frequent "abandonded transaction" errors on multiple high-volume repositories at Mozilla. This commit effectively reverts e9646ff34d55 and 1bfb9a63b98e to restore the old behavior. I agree with the principle that I/O errors shouldn't be ignored. That makes this change... unfortunate. However, our hands are tied for what to do on stable. I think the proper solution is for the ui's behavior to be configurable (possibly via a context manager). During critical sections like transaction rollback and abort, it should be possible to suppress errors. But this feature would not be appropriate on stable.