Select2 fix #3854 to center the search in admin area in ie, firefox and chrome

I did some more fixes to center the search box in different browsers:

Was in Chrome:
![chrome-current](https://f.cloud.github.com/assets/493547/1319906/cd62d376-3322-11e3-9447-018e424cc672.png)

Was in IE9:
![ie9-current](https://f.cloud.github.com/assets/493547/1319910/2aed0066-3323-11e3-8189-7ba328882d56.png)

After fixes it is:
Chrome:
![chrome-fixed](https://f.cloud.github.com/assets/493547/1319911/39e08a7a-3323-11e3-9498-86b50b2afb80.png)

Firefox:
![firefox-fixed](https://f.cloud.github.com/assets/493547/1319912/3f87e4aa-3323-11e3-833b-f3397cf266db.png)

IE9:
![ie9-fixed](https://f.cloud.github.com/assets/493547/1319915/6efee2ce-3323-11e3-83c3-e50627c47af7.png)