Fix broken example of csv.reader use (it returns an iterator, which isn't

indexable) by using the same 'for' construct as all other examples. (Also
emphasizes that reading from a random iterable is no different than reading
from a file.)

Doc/lib/libcsv.tex

@@ -421,7 +421,8 @@ easily be done:
 
 \begin{verbatim}
 import csv
-print csv.reader(['one,two,three'])[0]
+for row in csv.reader(['one,two,three']):
+    print row
 \end{verbatim}
 
 The \module{csv} module doesn't directly support reading and writing