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.

Unit tests pass.