Fix some markup nits.

Doc/tut/tut.tex

@@ -1819,9 +1819,11 @@ item, then to the result and the next item, and so on.  For example,
 0
 \end{verbatim}
 
-Don't use this example's definition of \code{sum}: since summing numbers
-is such a common need, a built-in function \code{sum(\var{sequence})} is 
-already provided, and works exactly like this\versionadded{2,3}.
+Don't use this example's definition of \function{sum()}: since summing
+numbers is such a common need, a built-in function
+\code{sum(\var{sequence})} is already provided, and works exactly like
+this.
+\versionadded{2.3}
 
 \subsection{List Comprehensions}