This used to be done whenever stdin was interactive. Now we only do
it when the -i flag is given. Also (and this is the real reason for
this fix) we explicitly allocate a buffer -- this seems to be
necessary on Windows.
even if it isn't. Changes:
- set the global flag Py_InteractiveFlag when -i is given
- call Py_FdIsInteractive() instead of isatty()
- make stdin unbuffered, too, when using -u
- make stdin and stdout line buffered, when stdin is interactive and not -u
Note that setting the environment variable PYTHONINSPECT does not have
these extra effects of -i. (Should it?)
Unlike Lee's changes, I don't set change the prompt to go to stderr
when -i is given.