[Cairo] Text APIs round 2

[Keith Packard]

Around 16 o'clock on Aug 15, Owen Taylor wrote:

> I suggested it because dx is a bit obscure and it is called 'width'
> in Postscript and in core X (that's what XTextWidth() gives you)

Sorry for being oblique; I like 'width' better too, but we do need to make 
sure the extents structure uses the same term for the same value.  The 
Render (and Xft) mess should be avoided.

-keith