Libjasper is not really maintained any more, and has been dropped by
various Linux distributions over the years.

GdkPixbuf has not enabled the JPEG2000 loader by default in many years,
relying on downstream distributors to do so if they also shipped
libjasper. This means that it's unlikely anybody has relied on GdkPixbuf
to load a JPEG2000 image for the past 3 to 5 years, if at all.

The only other option for loading JPEG2000 images is to use OpenJPEG,
and for that there is an out of tree GdkPixbuf module available:

https://notabug.org/necklace/jp2-pixbuf-loader

Fixes: #152, #137