Update two of the \indexsubitem values to use singular rather than plural form

of "variable": each individual variable should be identified as a single
variable and not a collection in the index.

Doc/lib/libbasehttp.tex

@@ -49,7 +49,7 @@ from the request. For example, for the request \code{SPAM}, the
 the relevant information is stored into instance variables of the
 handler.
 
-\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler instance variables)}
+\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler instance variable)}
 
 \code{BaseHTTPRequestHandler} has the following instance variables:
 
@@ -88,7 +88,7 @@ Proper adherance to the HTTP protocol must be used when writing
 to this stream.
 \end{datadesc}
 
-\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler class variables)}
+\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler class variable)}
 
 \code{BaseHTTPRequestHandler} has the following class variables:
 

Doc/libbasehttp.tex

@@ -49,7 +49,7 @@ from the request. For example, for the request \code{SPAM}, the
 the relevant information is stored into instance variables of the
 handler.
 
-\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler instance variables)}
+\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler instance variable)}
 
 \code{BaseHTTPRequestHandler} has the following instance variables:
 
@@ -88,7 +88,7 @@ Proper adherance to the HTTP protocol must be used when writing
 to this stream.
 \end{datadesc}
 
-\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler class variables)}
+\renewcommand{\indexsubitem}{(BaseHTTPRequestHandler class variable)}
 
 \code{BaseHTTPRequestHandler} has the following class variables: