I investigated icon scaling a bit last night, and noticed that we continuously
scale down stock button images from 24x24 to 20x20, and mime type icons (for the
file chooser) from 48x48 to 16x16 - even though Bluecurve has 20x20 stock icons
and 16x16 mimetypes, they are just not mentioned in the index.theme file.

We should make sure that the index.theme file lists all subdirectories.
Doing that has 3 benefits:

a) less cycles wasted with scaling icons
b) less memory wasted, since we can use the unscaled icons from the cache,
   which are shared
c) possibly better icons, since the existing Bluecurve icons are probably
   not just scaled down versions