Icon-theme-spec update for scaled icons

[Alexander Larsson]

> On Tue, 2013-07-02 at 15:51 +0200, Alexander Larsson wrote:
> > + Icons can have a target scale, describing what scale factor + they
> > are designed for.
> 
> Could you define "scale factor"? Something such as "High-DPI (> 200 dpi)
> screens would use a higher scale factor than the default 1x".

I don't think we want to be in the business of deciding when scaled
icons should be used, but we could say "for example...".