[gthumb-list] simplifying the raw_files extension

["Dr. Michael J. Chudobiak" <mjc avtechpulse com>]

Paolo and everyone,

The raw_files extension could be simplified a lot. Some suggestions:

1) Delete the HDR code. It supposedly converts files in a cache using 
pfstools. However, I don't think it has ever worked in the 3.x series, 
because image/x-hdr is not registered by 
gth_main_register_image_loader_func_v.

2) Rely on libraw, and remove the dcraw fallback. I think libraw is 
available for all major distros, so there is no point to the 
caching/dcraw approach.

3) The only mime type that should be handled by the raw_files is 
"image/x-dcraw". The other RAW types are all sub-types of this.

Also:

4) Any objection if I add "JPEG" and "RAW" filters? These would be handy 
for the importer - for example: 
https://bugzilla.gnome.org/show_bug.cgi?id=732026, where the user wants 
to ignore the *.bmp files.


Is it OK if I implement these changes, Paolo?

- Mike