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 applied. Differential Revision: https://phab.mercurial-scm.org/D10708