Update Backbone to version 1.1.2.

props gcorne.
fixes #27182.
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Bump.

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Correct PHPDoc return description for `get_boundary_post()`.

Props ericlewis.
Fixes #22950.

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Build: Update version of grunt-autoprefixer devDependency.

The update includes a new version of Autoprefixer which now supports the `ms-touch-action` prop for IE10.
Run `grunt autoprefixer:core` to re-add the missing props in media-view.css.
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