Tabindex not brought into focus

[fauverism]

When launching a modal with links and/or buttons contained within the modal if you attempt to use the tab key in order to navigate through the links you are unable to do so. The focus remains in the DOM for the main-content.

Steps to recreate

1. Launch the live demo modal on http://getbootstrap.com/2.3.2/javascript.html#modals
2. Pressing the tab key will allow you to rotate thru the links/buttons within the modal.
3. If you visit http://angular-ui.github.io/bootstrap/#/modal you'll notice that there isn't a tabindex on the modal. If a tabindex is put on the links/buttons the same functionality is not present.

[pkozlowski-opensource]

Yes, this needs to be fixed but is duplicate of #738