Switch from Bootstrap 2.3.1 to current v3 RC2.
Include Glyphicons.
I don't think we need a local copy of the select2 assets, but I might be wrong.
Update markup to fit Bootstrap 3 RC2:

 * form.form-horizontal is quite markup heavy, so I chose to use the default vertical form layout
 * .control-group became .form-group
 * appended and prepended buttons now need a wrapper span.input-group-btn; their .btn needs an additional .btn-default to look as intended
 * .input-group became obsolete (from what I understand after spending a few minutes with this stuff)
 * i.icon became span.icon
 * not sure what to do about width definitions for select2, for now it's a mix between the old 400px and 100%
 * as .input-append and .input-prepend have been removed in Bootstrap 3 RC2, I added a .select2-bootstrap-append and .select2-bootstrap-prepend to go with .input-group for easy distiction
Not too bad for a first shot at the CSS:

 * adjust select2 height and line-height to fit the now slightly bigger default Bootstrap 3 RC2 inputs
 * remove background for the dropdown arrow for select2 v3.4.1 (personal stylistic preference)
 * basic support for appended and prepended buttons via .select2-bootstrap-prepend/-append
Add demo page for select2 v3.4.2. Not too bad, but .select2-container-active now remains set after closing the select2 dropdown … which looks a bit weird. Not sure how to handle that properly.
Move from rgba-border-color to solid hex.
.select2-drop-active border-color now matches .select2-choice.