Support for new items in set type

[Prateek]

> I don't see where your SeaSet class is used.
>
Actually that is the point. According to the hotshot profile, the
problem code doesn't use the SeaSet implementation. Yet that same code
was running much faster earlier. I tried multiple time (2-3 times).
>From what I can fathom, nothing else changed - just the set
implementation.

It seems obvious that the read() call in the __readTableHeader method
is blocking for longer periods although it isn't exactly obvious why
that might be.

I was hoping someone with an idea of Python-C interaction could shed
some light on this. I'm on a different computer right now, I'll log
back in later and post more code if that helps.

Again, thanks to anyone who can help.

Prateek