fix set tabindex to all the node

if set tabindex to all the node will cause blue highlight border around the dom if the dom created by virtualize is clicked

for example: the blue border isnt what I want
![d492c369-9e0a-447e-a93d-1a56a10cd403](https://cloud.githubusercontent.com/assets/3351878/5538475/7119e3ae-8aef-11e4-92bf-33205459a8d6.png)