Ah, that explains it. I just looked at the makepanda source and realised that one now also has to add --use-direct to include the direct tree in the build.
You don’t need to use CVS to try the 1.8 build. You can just download and install it from this page:
panda3d.org/download.php?sdk&version=devel
Although it is never guaranteed to be stable at any point in time.