replace time reference with system reference

Author: vladak

file-api.tex

@@ -1209,7 +1209,7 @@
 \item Only the owner of a file can change its mode.  Mode like
 \texttt{rw-rw-rw-} has nothing to do with that.
 \item In some implementations, it was possible to pass the file ownership to
-someone else.  Today this is usually not allowed.  Just think about how you
+someone else. On modern Unixes this is usually not allowed.  Just think about how you
 could work around a per-user filesystem quota with this.
 \end{itemize}