Use Exif Data to check the image type, Do not rely on extention
Merge pull request #2788 from exussum12/exif_imagetype

Use Exif Data to check the image type, Do not rely on extention
Refactored last merge, updated version number, updated tests.
User exif_imagetype (if available) to determine proper file extensions.
Merge branch 'master' of https://github.com/blueimp/jQuery-File-Upload