Behavior is now like all xinerama related options are enabled.
There seems to be no valid reasons to run multi screen without
xinerama support and even if a user would wish to do so she can
just disable xinerama in xorg.conf.
Furhtermore thanks to KWin scripting it is possible to achieve the
behavior as it used to be with the options disabled. E.g. it is
possible to span a window in fullscreen mode over all screens.
This change is in accordance to the discussion on kwin and plasma
mailinglists:
http://mail.kde.org/pipermail/plasma-devel/2012-January/018542.html