The counts/counter moniker emerged from the python-dev discussion and
I'm basically happy with it since the typical usage is c=Counter(myseq)
with no other non-dict accesses (mostly just c[elem]+=1 and print
c[elem]).  It's a simple counter with a dict interface so the name
shouldn't suggest anything more complicated than that.

To me, MultiSet or CountingSet is too offputtingly computer-sciency and
misleadingly suggests a set-like API instead of a dict interface. I know
several programmers who don't know the terms, bag or multiset, but they
intuitively understand what a counter does.  Am open to calling it a Bag
but I rather like the self-descriptiveness and simplicity of Counter.  

As noted previously, standalone unittests are forthcoming (and a doc
patch).  Wanted to get the API and sample use cases worked-out first.

Thanks for looking at the initial patch.