Update comments about the performance of xrange().

Doc/lib/libstdtypes.tex

@@ -884,8 +884,8 @@ xrange object will always take the same amount of memory, no matter the
 size of the range it represents.  There are no consistent performance
 advantages.
 
-XRange objects have very little behavior: they only support indexing
-and the \function{len()} function.
+XRange objects have very little behavior: they only support indexing,
+iteration, and the \function{len()} function.
 
 
 \subsubsection{Mutable Sequence Types \label{typesseq-mutable}}

Objects/rangeobject.c

@@ -113,8 +113,8 @@ PyDoc_STRVAR(range_doc,
 "xrange([start,] stop[, step]) -> xrange object\n\
 \n\
 Like range(), but instead of returning a list, returns an object that\n\
-generates the numbers in the range on demand.  This is slightly slower\n\
-than range() but more memory efficient.");
+generates the numbers in the range on demand.  For looping, this is \n\
+slightly faster than range() and more memory efficient.");
 
 static PyObject *
 range_item(rangeobject *r, int i)