Fix availability declaration for stat module; report by Barry Scott

<barry@scottb.demon.co.uk>.

Doc/lib/libstat.tex

@@ -2,7 +2,7 @@
          Interpreting \function{stat()} results}
 
 \declaremodule{standard}{stat}
-  \platform{Unix}
+  \platform{Unix, Windows}
 \modulesynopsis{Utilities for interpreting the results of
   \function{os.stat()}, \function{os.lstat()} and \function{os.fstat()}.}
 \sectionauthor{Skip Montanaro}{skip@automatrix.com}