Modular drivers

Hello!

While looking into native support for hylafax in libgnomeprint, I
realized that drivers are not yet modular. I supposed they were intended
to be modular, but nobody ever got around implementing it.

I posted a patch at http://bugs.gnome.org/show_bug.cgi?id=168890 that
implements modular drivers. It moves the postscript/pdf/svg/... drivers
into the subdirectory libgnomeprint/drivers. 

Users can select which drivers to compile
(--with-drivers=postscript,pdf). 

And other projects can now implement their own drivers outside of
libgnomeprint to be used together with libgnomeprint.

Regards
-- 
Lutz Müller <[email protected]>