This adds `stderr` and `stdin` control for `get_input()`, `get_pass()`, `confirm()`, and `confirm_select()` utilities. When hooked up properly, this enables unit tests to automate code paths that require user input. If `stdin` is a TTY, these will prompt the user for input as normal. Otherwise, they'll read a line from `stdin`. This allows for scripting inputs. While here, a few additional tweaks were made to these very old utilities: * `confirm()` no longer uses a private method in `distutils` to check for Yes/No input strings. Instead, the checks are now under our control. * `confirm()` and `confirm_select()` now show bad user input in quotes. Unit tests were also added for all these functions.