fix some markup errors

Doc/lib/libbase64.tex

@@ -85,7 +85,7 @@ security purposes, the default is \code{False}.
 letter O (oh), and for optional mapping of the digit 1 (one) to either
 the letter I (eye) or letter L (el).  The optional argument
 \var{map01} when not \code{None}, specifies which letter the digit 1 should
-be mapped to (when map01 is not \var{None}, the digit 0 is always
+be mapped to (when \var{map01} is not \code{None}, the digit 0 is always
 mapped to the letter O).  For security purposes the default is
 \code{None}, so that 0 and 1 are not allowed in the input.
 

Doc/lib/liblogging.tex

@@ -1528,7 +1528,7 @@ which, together with \var{msg}, makes up the user message; and
 \var{exc_info} is the exception tuple obtained by calling
 \function{sys.exc_info() }(or \constant{None}, if no exception information
 is available). The \var{func} is the name of the function from which the
-logging call was made. If not specified, it defaults to \var{None}.
+logging call was made. If not specified, it defaults to \code{None}.
 \versionchanged[\var{func} was added]{2.5}
 \end{classdesc}
 

Doc/lib/libstdtypes.tex

@@ -1496,7 +1496,7 @@ provided and \var{k} is not in the map, \code{None} is returned.
 
 \item[(5)] \function{setdefault()} is like \function{get()}, except
 that if \var{k} is missing, \var{x} is both returned and inserted into
-the dictionary as the value of \var{k}. \var{x} defaults to \var{None}.
+the dictionary as the value of \var{k}. \var{x} defaults to \code{None}.
 
 \item[(6)] \function{popitem()} is useful to destructively iterate
 over a dictionary, as often used in set algorithms.  If the dictionary
@@ -1855,7 +1855,7 @@ define a runtime context:
   expection that occurred should be suppressed. If an exception
   occurred while executing the body of the \keyword{with} statement, the
   arguments contain the exception type, value and traceback information.
-  Otherwise, all three arguments are \var{None}.
+  Otherwise, all three arguments are \code{None}.
 
   Returning a true value from this method will cause the \keyword{with}
   statement to suppress the exception and continue execution with the

Doc/lib/libxmlrpclib.tex

@@ -287,7 +287,7 @@ single request.
 
 Create an object used to boxcar method calls. \var{server} is the
 eventual target of the call. Calls can be made to the result object,
-but they will immediately return \var{None}, and only store the
+but they will immediately return \code{None}, and only store the
 call name and parameters in the \class{MultiCall} object. Calling
 the object itself causes all stored calls to be transmitted as
 a single \code{system.multicall} request. The result of this call