be fixed for good until I look at the last bit of code that has not been
examined yet, which is the plane intersection code. I want the errors to be
much less than they are now, even though the disappearing_sliver* tests are
now working.
git-svn-id: svn://svn.icculus.org/gtkradiant/GtkRadiant/trunk@378 8a3a26a2-13c4-0310-b231-cf6edde360e5