Polls can now have a policy on how votes will be tabulated

Up until now, only members on the site could vote in a poll. Now, each poll can have one of three policies:

1. **None**: anybody can vote any number of times. This is the default case
2. **Once per Session**: Anybody can vote, but only one time per session. This should cut down on people stuffing the ballot box.
3. **Members Only**: Only members of the site can participate in the poll (but anyon can view the results).

In most cases, this will allow anyone to participate in a poll (and should lead to some interesting results). Enjoy!