Common gotchas upgrading from 4.0 -> 4.2

[Jasper Huijsmans]

Brian J. Tarricone wrote:
...
> 
> 1) include a small .svg icon with libxfcegui4 that gets installed in a known
> location, and try to open it on XfceIconTheme's class_init().  if it fails,
> we don't have SVG support.
> 

Very cunning. I considered validating icons, but rejected it because of 
obvious performance issues. I like this. Should be 100% accurate, 
shouldn't it?