[Fontconfig] Regularizing contains operator semantics

[Keith Packard]

Around 10 o'clock on Jul 12, Owen Taylor wrote:

> Can you give a concrete example? As Keith said, if you specify
> a font explicitly, you'll get that font for every character
> it contains.

I thought the problem mentioned was that applications were using lang to 
restrict the presented list of available fonts in some context.  I know 
Mozilla does this when selecting preferred fonts for language groups; I 
can believe that other apps also do this; perhaps we should find a way to 
deprecate this activity.  The Mozilla behaviour was inherited from the 
core font listing techniques and so is not specific to it's interactions 
with fontconfig.

-keith