Fix: Import Less files even if they do not have the .less extension

<a href="https://github.com/s7eph4n"><img src="https://avatars.githubusercontent.com/u/2829850?v=2" align="left" width="96" height="96" hspace="10"></img></a> **Issue by [s7eph4n](https://github.com/s7eph4n)**
_Saturday Aug 16, 2014 at 23:05 GMT_
_Originally opened as https://github.com/oyejorge/less.php/pull/159_

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@import directives should work even if the .less file extension is not present.

see http://lesscss.org/features/#import-directives-feature-file-extensions:
"If it does not have an extension, .less will be appended and it will be included as a imported Less file."

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_**[s7eph4n](https://github.com/s7eph4n)** included the following code: https://github.com/oyejorge/less.php/pull/159/commits_