util: avoid echoing the password to the console on Windows py3 (issue6446)
The getpass.getpass() implementation on Windows first checks if sys.stdin
and sys.__stdin__ are the same object. It's not on py3 because the former is
replaced in dispatch.py with something that doesn't normalize '\n' to '\r\n'.
When they aren't the same object, it simply calls sys.stdin.readline() instead
of the mscvrt functions that read the input characters before they are echoed.
This simply copies the getpass.win_getpass() implementation without the stdin
check, and byteifies around the edges. I'm not sure if there's a reasonable
replacement for the check that we could implement. When echoing input into the
hg command, the ui.interactive() check causes ui.getpass() to bail before
getting here. If the proper config switches are used to bypass that and call
this, the process stalls until '\n' is input into the console. So there could
be a deadlock here when run by another command if the wrong config settings are
Differential Revision: https://phab.mercurial-scm.org/D10708