Wrong imagetype in export

[Rillke]

The export defaults the imagetype to image/jpeg if the file does not end in gif or png.

However, you can upload foo.PNG. A perfectly valid PNG file that will be classified as <fieldlabel>imagetype</fieldlabel><fieldentry>image/jpeg</fieldentry> in the exported XML.

Maybe use gd here to determine the type as the rest of the plugin does or make the regexp case insensitive?

[Rillke]

also you don't really need the .* part of the regexp (as it basically says something or nothing; a never referenced ταυτολογία), do you?