enhanced chunked

I've found this recipe at python-ideas, where it was suggested by Peter Otten. You may want to time its performance against your current version of chunked(), but I think it should be faster. Also, Wolfgang Maier's proposal of the strict parameter to turn on error handling looks like a good idea to me.
This is the original thread at python-ideas:
http://thread.gmane.org/gmane.comp.python.ideas/20113