Documented imageflip(), available as of PHP 5.5.0 using LibGD

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@329873 c90b9560-bf6c-de11-be94-00142212c4b1
Fix svn:props

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@329874 c90b9560-bf6c-de11-be94-00142212c4b1