Use specialized exception for unsupported file formats

[GoogleCodeExporter]

Today, ImageMetadataReader will throw an ImageProcessingException() for 
unspported file format (using throw new ImageProcessingException("File format 
is not supported")).

It would be helpful if we could catch this error specifically, since we want 
different error handling for this compared to other (unknown errors)

The simplest (and probably also best :-)) way would be to create a subclass 
"UnsupportedFileFormatException" and throw that instead.

Original issue reported on code.google.com by eirik.ly...@gmail.com on 26 Feb 2014 at 12:45