bug#17839: 24.4.50; read-passwd echoes password input in non-interactive sessions

[Eli Zaretskii]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: monnier@iro.umontreal.ca,  schwab@suse.de,  17839@debbugs.gnu.org,  
> swiesner@lunaryorn.com
> Date: Fri, 11 Jul 2014 14:43:10 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Alternatively, shall we add (disable|enable)_echo functions to sysdep.c?
> >
> > Yes, please.  This will make emulating termios for Windows easier.
> 
> I've moved the code to the new function suppress_echo_on_tty of
> sysdep.c. For resetting the tty, no new function was necessary.

Thanks.  I added implementation for MS-Windows.

The result is not 100% satisfactory, as one needs to press RET twice
to finish the input, and it looks like some garbage is left in the
input buffer, since the following (normal) input gets something
strange.  A workaround is to press C-z, which produces EOF, instead of
RET, when password entry is finished.

I also needed a change in minibuf.c to end the reading loop on CR, not
just a newline.  If this is bad news for Posix platforms, we can make
that code conditional on Windows.