clean up indexing for None, NotImplemented

closes SF bug #820344

Doc/api/concrete.tex

@@ -85,7 +85,7 @@ This section describes Python type objects and the singleton object
 
 \subsection{The None Object \label{noneObject}}
 
-\obindex{None@\texttt{None}}
+\obindex{None}
 Note that the \ctype{PyTypeObject} for \code{None} is not directly
 exposed in the Python/C API.  Since \code{None} is a singleton,
 testing for object identity (using \samp{==} in C) is sufficient.

Doc/ref/ref3.tex

@@ -134,8 +134,7 @@ This object is accessed through the built-in name \code{None}.
 It is used to signify the absence of a value in many situations, e.g.,
 it is returned from functions that don't explicitly return anything.
 Its truth value is false.
-\ttindex{None}
-\obindex{None@{\texttt{None}}}
+\obindex{None}
 
 \item[NotImplemented]
 This type has a single value.  There is a single object with this value.
@@ -144,8 +143,7 @@ Numeric methods and rich comparison methods may return this value if
 they do not implement the operation for the operands provided.  (The
 interpreter will then try the reflected operation, or some other
 fallback, depending on the operator.)  Its truth value is true.
-\ttindex{NotImplemented}
-\obindex{NotImplemented@{\texttt{NotImplemented}}}
+\obindex{NotImplemented}
 
 \item[Ellipsis]
 This type has a single value.  There is a single object with this value.

Doc/ref/ref6.tex

@@ -48,7 +48,7 @@ function and the resulting string is written to standard output (see
 section~\ref{print}) on a line by itself.  (Expression statements
 yielding \code{None} are not written, so that procedure calls do not
 cause any output.)
-\ttindex{None}
+\obindex{None}
 \indexii{string}{conversion}
 \index{output}
 \indexii{standard}{output}