[Fontconfig] [Xft] text width of monospaced fonts

[Keith Packard]

> Is there any way to find out whether the font is monospaced to be able
> to calculate the text width manually instead of calling
> XftTextExtents8 all the time?

You can get the FC_SPACING value out of the pattern and check to see what
the value is.  Note that current fontconfig actually walks through the
font to check all of the spacing values so that this setting should be
accurate.

-keith