Default font in 2.5.26 on Windows

[Bertalan Fodor]

In font.scm there is:
(add-pango-fonts n 'roman "Century Schoolbook L" factor)
   (add-pango-fonts n 'sans "Luxi Sans" factor)

But on Windows these fonts are not present. So Pango goes back to some 
default: Bitstream Vera Sans for both. That's not optimal.

If I change font.scm to:
   (add-pango-fonts n 'roman "serif" factor)
   (add-pango-fonts n 'sans "sans-serif" factor)

it will use pango's preferences for fonts.

A user question: how to change globally the meaning of the family setting?

Bert