[Python-3000] Reverse file iteration patch updated

[Mark Russell]

I posted a patch (http://bugs.python.org/issue1677872) a while ago to  
add support for reverse iteration through text files - i.e. making  
this work:

      for line in reversed(open(path)):
          print line

It steps through the file backwards a line at a time, without reading  
the entire file contents first - useful for scanning backwards though  
big log files for example.

Christian Heimes commented that there's a reasonable chance of it  
being accepted, so I've updated the patch to work against the current  
source, as well as adding unit tests and documentation.

Mark Russell