[FEATURE] New setting "ajaxValidationCallback" (resolves #57529)

git-svn-id: https://svn.typo3.org/TYPO3v4/Extensions/formhandler/trunk@84572 735d13b6-9817-0410-8766-e36946ffe9aa
[TASK] Compatibility fixes for 6.2 (#55783)

git-svn-id: https://svn.typo3.org/TYPO3v4/Extensions/formhandler/trunk@84579 735d13b6-9817-0410-8766-e36946ffe9aa