Update lessphp to 261f1bd28

From https://github.com/leafo/lessphp/blob/261f1bd28f/lessc.inc.php

Changes, 6e8e724fc7..261f1bd28f:
* 261f1bd Merge pull request #480 from atdt/master
* 0f85200 Miscellaneous small touch-ups
* 5504066 Improve handling of /* comments */ when 'preserveComments' is set
* 667702c Make function helpers public


Bug: 54673
Change-Id: Ib6bc76736d460081dc8f48aee09ca32066dae296
Merge "Update lessphp to 261f1bd28"