This is kinda a lame little hack to the Aurora engine to remove the scrollbar trough gradient. This patch doesn't add any features... I just commented out a couple lines. It looks okay with all "pure" Aurora themes (see first screenshot)... You might want to use GtkRange::trough-border=1 (at least) in gtkrc. I actually did this to make it look better with Clearlooks themes (see second screenshot).
tar xfz aurora-1.4.tar.gz
patch -p1 < ../aurora-flat_scrollbar_trough.patch
./configure --prefix=/usr --enable-animation
make install (or checkinstall for deb users)