speed x2

This minor change reduces time of `init` by half. The benchmarks I ran invoked `multiSelect('refresh')` on 2 select tags, each w/ 2000 options, recreated 4 times in 50 ms intervals. This branch and master both took 7-8 seconds to complete (Chrome 27). With this change it comes down to around 4 seconds on perf2.  I made a JS fiddle to share ... http://jsfiddle.net/ridiculous/JdALv/5/

The element creation and insertion in the main loop is costly. I think speed to improve a lot if we can implement that differently. I started work on something and then found this branch. 

You may see more pull requests from me :)