svnlook.py - add iterator interface

[anatoly techtonik]

Hi,

It would be more handy if svnlook.py API also returned iterators to
avoid eating memory for processing every commit:

http://svn.apache.org/viewvc/subversion/trunk/tools/examples/svnlook.py?revision=1295006&view=markup

Please, CC.
--
anatoly t.