Standardize GetTokenInformation() error reporting.

Commit c22650cd sparked a discussion
about diverse interpretations of "token user" in error messages.  Expel
old and new specimens of that phrase by making all GetTokenInformation()
callers report errors the way GetTokenUser() has been reporting them.
These error conditions almost can't happen, so users are unlikely to
observe this change.

Reviewed by Tom Lane and Stephen Frost.