Unexpected behaviour when using toFile without an extension matching output format

[GoogleCodeExporter]

Take this small code block:

File inputFile = new File("...");
File outputFile = File.createTempFile("thumbnail", null);
Thumbnails.of(inputFile).size(100,100).outputFormat("jpg").toFile(outputFile);

My expected result is that outputFile contains the thumbnail, which I think is 
reasonable and in line with the javadocs of toFile. However, Thumbnailator 
writes the thumbnail to a new file with .jpg appended, which isn't exposed 
anywhere, so my code in principle has no way of accessing the thumbnail without 
knowledge of the internal implementation.

Obviously this is easy enough to work around by creating the temp file with a 
.jpg extension, but this really shouldn't be needed.

Original issue reported on code.google.com by bjmac...@gmail.com on 19 Feb 2014 at 8:15