Add isset() check to reset setting

Since reset setting can be either nonexistent (null) or "true", it needs to be checked with isset() to avoid PHP notice.
Minor correction to a comment
Store REMOTE_ADDR (user's IP) instead of SERVER_ADDR

This way each user is (theoretically) blocked from voting multiple times instead of automatically blocking all users with matching user agent string.
Wrap vote count of each option with <span></span>

This makes styling div.percentage elements easier, as you can set styles (including padding) for content without affecting parent element.
Merge pull request #1 from teppokoivula/master

Use REMOTE_ADDR instead of SERVER_ADDR, add isset() check, wrap vote count in span and make one comment correction