[ 1243288 ] Misuse of "it's"

Doc/ref/ref2.tex

@@ -349,7 +349,7 @@ trailing underscore characters:
 
 \item[\code{__*__}]
   System-defined names.  These names are defined by the interpreter
-  and it's implementation (including the standard library);
+  and its implementation (including the standard library);
   applications should not expect to define additional names using this
   convention.  The set of names of this class defined by Python may be
   extended in future versions.