Fix using input instead of select elements with input-append

Thank you very much for the very nice styles! When I am using an ```input```instead of a ```select``` element (e.g. because of select2's ajax feature doesn't work with ```input``` elements), then the resulting dropdown have some ugly space:

![input_append](https://f.cloud.github.com/assets/17513/334551/06b47308-9c76-11e2-8c38-31d14979b4c9.png)

Using the appended styles fixes the problem:

![input_append_fixed](https://f.cloud.github.com/assets/17513/334556/1706c0e4-9c76-11e2-914a-bf2a74231599.png)

Explanation of fix:  Bootstrap sets ```.input-append input{position:relative}``` which overrides ```.select2-offscreen{position: absolute}``` .