Add an index entry for the discussion of PyEval_CallObject().

This is related to SF bug #485165.

Doc/ext/extending.tex

@@ -509,14 +509,15 @@ the presence of \NULL{} pointers (but note that \var{temp} will not be
 section~\ref{refcounts}, ``Reference Counts.''
 
 Later, when it is time to call the function, you call the C function
-\cfunction{PyEval_CallObject()}.  This function has two arguments, both
-pointers to arbitrary Python objects: the Python function, and the
-argument list.  The argument list must always be a tuple object, whose
-length is the number of arguments.  To call the Python function with
-no arguments, pass an empty tuple; to call it with one argument, pass
-a singleton tuple.  \cfunction{Py_BuildValue()} returns a tuple when its
-format string consists of zero or more format codes between
-parentheses.  For example:
+\cfunction{PyEval_CallObject()}.\ttindex{PyEval_CallObject()}  This
+function has two arguments, both pointers to arbitrary Python objects:
+the Python function, and the argument list.  The argument list must
+always be a tuple object, whose length is the number of arguments.  To
+call the Python function with no arguments, pass an empty tuple; to
+call it with one argument, pass a singleton tuple.
+\cfunction{Py_BuildValue()} returns a tuple when its format string
+consists of zero or more format codes between parentheses.  For
+example:
 
 \begin{verbatim}
     int arg;