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The project page still states that jquery.flexslider.js is optional - "The first two files are required and the last is optional (required for javascript debugging)". The README does say it's required, although it still suggests it's only for debugging, while it's necessary for the library to be recognized as well:
"FlexSlider library not found. Please consult the README.txt for installation instructions." on Status report page when jquery.flexslider.js is missing.
FlexSlider library version 2.2.2 in sites/all/libraries/flexslider, using Libraries 2.1.