Fixing issue #28, off-by-one error

We have fixed the issue #28, at least what we understand. 

We were scratching our head multiple times about jquery.easydropdown.js:322 and what you had in mind with this construct. We didn't come to any explanation. Why don't you exclude options with class='label' from the index calculation? On the other hand, whenever we wanted to select an option by a string, we ended up with the option being selected before the intended options. Here is definitely sth. off.

It would be great if you could enlighten our mind or merge this pull request. Thanks.