Added index entry for "file objects"; this is appearantly referenced

somewhere in the Reference Manual, and someone tried to locate it via
the index.  Report on the omission by Stefan Franke
<sfranke@cdc-group.com>.

Doc/lib/libstdtypes.tex

@@ -710,15 +710,16 @@ exactly one ellipsis object, named \code{Ellipsis} (a built-in name).
 
 It is written as \code{Ellipsis}.
 
-\subsubsection{File Objects \label{bltin-file-objects}}
+\subsubsection{File Objects\obindex{file}
+               \label{bltin-file-objects}}
 
-File objects are implemented using \C{}'s \code{stdio} package and can be
-created with the built-in function \function{open()} described Section
+File objects are implemented using \C{}'s \code{stdio}
+package and can be created with the built-in function
+\function{open()}\bifuncindex{open} described Section
 \ref{built-in-funcs}, ``Built-in Functions.''  They are also returned
 by some other built-in functions and methods, e.g.,
 \function{posix.popen()} and \function{posix.fdopen()} and the
 \method{makefile()} method of socket objects.
-\bifuncindex{open}
 \refbimodindex{posix}
 \refbimodindex{socket}