Changes the behavior of Sass's @import directive to only import a file once.
This plugin changes the behavior of Sass's `@import` directive so that
if the same sass file is imported more than once, the second import
will be a no-op. This allows dependencies to behave how most people
expect them to behave and provides a considerable performance improvement
for some sass projects.
**Note**: Although this plugin is maintained by compass, it can be used
without compass in any Sass-based project.
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