Cygwin: seteuid: use Kerberos/MsV1_0 S4U authentication by default
- This simple and official method replaces cyglsa and "create token"
methods. No network share access, same as before.
- lsaauth and create_token are disabled now. If problems crop up,
they can be easily reactivated. If no problems crop up, they
can be removed in a while, together with the lsaauth subdir.