The TIFF loader need to exclude CR2 files.

When it tries to open CR2 files using libtiff, it fails because it is not a TIFF compliant file.

The following signature should be added to the GdkPixbufModulePattern list in the tiff pixbuf loader:
{"II* \020   CR\002 ", "   z zzz   z", 0 }

Same problem with arise with other TIFF-like raw files, but is not as easy.

(I use that signature with a level of confidence of 100 in my libopenraw pixbuf loader)