... in a style with family "paragraph", as detected by a
--with-export-validation build due to the unit test added yesterday.

So use the loext namespace for the style:graphic-properties element,
and also omit it entirely (and rely on the style:paragraph-properties
attributes fo:background-*) if the ODF version is set to 1.2 or 1.1.

Also adapt a previous check that was missing the "drawing-page" style
family, where the style:graphic-properties is allowed (commit
9746dc9a)

(regression from 7d9bb549)

Change-Id: Iedd66483f63020328bd61e1c1e19c62787b8ff6b