Bootstrap 2.3

Work-in-progress pull request for bug fixes and enhancements before our 3.0 release. Originally this was slated as 2.2.3, but since we added a feature, it gets the minor release.

#### Key changes

- **Updated makefile** to use local dependencies for easier dev setup.
- **Added carousel indicators!** Add the associated HTML and it automagically works.
- **Added [new justified navigation example](https://f.cloud.github.com/assets/98681/25869/5e2f812c-4afa-11e2-9293-501cd689232d.png).** This was previously an unlinked and unsupported example I snuck in back in October. Officially adding it via the 2.3 release.
- **Added sticky footer with fixed navbar example** because folks seem to have trouble adapting the default example.
- **Added `container` option to tooltips.** The default option is still `insertAfter`, but now you may specify where to insert tooltips (and by extension, popovers) with the optional container parameter.
- **Improved popovers** now utilize `max-width` instead of `width`, have been widened from 240px to 280px, and will automatically hide the title if one has not been set via CSS `:empty` selector.
- **Improved tooltip alignment on edges** with #6713.
- **Updated input groups** to make them behave more like default form controls. Added `display: inline-block;`, increased `margin-bottom`, and added `vertical-align: middle;`  to match `<input>` styles.
- **Improved accessibility for links in all components.** After merging #6441, link hover states now apply to the `:focus` state as well. This goes for basic `<a>` tags, as well as buttons, navs, dropdowns, and more.
- **Added print utility classes** to show and hide content between `screen` and `print` via CSS.
- **Upgraded to jQuery 1.9.** No changes were needed, but we did upgrade the included jQuery file to the latest release.
- **Moved changelog to be within the repo** instead of as a wiki page.
- Added `.horizontal-three-colors()` gradient mixin (with example in the CSS tests file).
- Added `.text-left`, `.text-center`, and `.text-right` utility classes for easy typographic alignment.
- Added `@ms-viewport` so IE10 can use responsive CSS when in split-screen mode.
- Tooltips now work with SVG.
- Updated to latest HTML5 shiv with a new local copy (within the repo) instead of the outdated Google Code version.
- Fixed z-index issues with navbar and carousel controls in the carousel example.
- Added support for `th` elements within `tbody` for `.table-rounded`.
- Removed `target-dir` from composer.json.
- Updated Holder.js from v1.6 to v1.9.
- Other miscellaneous CSS and docs bugfixes items.

#### Specifics

Get the full list by [viewing the closed issues](https://github.com/twitter/bootstrap/issues?labels=&milestone=18&page=1&sort=updated&state=closed), or peeping the [list of commits in this pull request](https://github.com/twitter/bootstrap/pull/6346/commits).

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