(GetPW): Add parameter to (dis)allow printing of Windows username.
Use defines instead of numerical constants where possible.
Try avoiding impersonation problem. Rearrange to print Windows
username only if it's different from Cygwin username.
(ChangePW): Use defines instead of numerical constants where possible.
(main): Call GetPW with additional parameter. Change error text.
* passwd.c (GetPW): Handle case of user-edited /etc/passwd
with cygwin_internal (CW_EXTRACT_DOMAIN_AND_USER, ...).
checking old password and called for changing password. If called
for checking old password, return non-zero only if password is surely
incorrect.
(main): Call ChangePW() with additional parameter.
