When doing a form POST with AJAX, file upload values can come across as empty strings and not part of the $_FILES array.
Fixed the FileInput to allow non-array values, which helps the AJAX case.
Example usage can be found here, under the "Partial Session Progress" example: https://github.com/cgmartin/ZF2FileUploadExamples
FileInput AJAX post fix
Merge branch 'hotfix/3199' into develop