[NTOS:SE] Fixes for NT tokens.
- SeIsTokenChild(): Correctly check whether a caller-provided token
is a child from the current process' primary token by looking at
its ParentTokenId member.
- Add a SeIsTokenSibling() helper to determine whether a caller-provided
token and the current process' primary token are siblings, by comparing
their ParentTokenId's and AuthenticationId's.
NOTE: Children tokens are created through CreateRestrictedToken();
sibling tokens are created through DuplicateToken() (amongst others).
See slide 49 of https://www.slideshare.net/Shakacon/social-engineering-the-windows-kernel-by-james-forshaw
or https://googleprojectzero.blogspot.com/2016/01/raising-dead.html
for some details.