* Default to using /dev/tty for the password prompt and input before
  falling back to sys.stdin and sys.stderr.
* Use sys.stderr instead of sys.stdout.
* print the 'password may be echoed' warning to stream used to display
  the prompt rather than always sys.stderr.
* warn() with GetPassWarning when input may be echoed.

a warning instead of failing with a termios.error.

argument to specify where to write the prompt.

Make sure we have a UNIX-compatible termios.
Apparently, McMillan Installer made a termios on windows
which caused unix_getpass() to be used instead of win_getpass().

Will backport.

default_getpass().  This should prevent hanging when it is called in
IDLE.

Fixes SF bug #455648.

docstrings into comments.

At import time, getpass will be bound to the appropriate
platform-specific function.  If the platform's echo-disabler is not
available, default_getpass, which prints the warning, will be used

exists.

Windows.  If sys.stdin doesn't appear to be a real file (characterized
by having a working fileno()), don't use any console specific methods
-- go straight to the default.

-- don't just die.

in the GNU readline history buffer which is not such a great idea.

the tty and the caller can deal with the interrupt.

In the windows version, recognize ^C and raise KeyboardInterrupt (not
sure if this is needed, but can't hurt).

Also contains getuser(), which returns the username (not prompting though).
These work on Unix and Windows!