change thumbnailer spec to fit better with xdg-basedir spec

[Martin Meyer]

GNOME currently has an open bug [1] which is aimed at using the XDG
basedir spec to eliminate some of the numerous folders in $HOME for
each user. I love this idea, and I've been following the bug closely.
One particular directory which can't be fixed currently is
~/.thumbnails. I've filed a bug [2] about this particular issue so I
wanted to bring it up here for discussion.

The thumbnailer spec [3] points to the ~/.thumbnails directory for the
cache of specific-sized thumbnails. Although I call them cache, it is
arguable that they may be user data. The issue I have is that the
basedir spec [4] specifies an environment variable $XDG_CACHE_HOME
which is intended as the base for all "user-specific non-essential
(cached) data". I feel that the thumbnail cache would fit in there. Is
there a chance of getting the spec changed to point to
$XDG_CACHE_HOME/thumbnails instead perhaps? Is it even open for
discussion?

Cheers,
Martin