src_configure fails on systems lacking GTK+; looking at the configure script, you probably need to add a 'gtk' USE flag, then DEPEND on x11-libs/gtk+ and set --with-gui= accordingly. Doesn't look like it automagically links against GTK+, but configure does fail if it's not there.
Also, src_test () { emake check || die } would appear to be near enough to the default (yours lacks the -j1 in the default) to be superfluous. Also, you don't seem to be using eutils. base.eclass does, but that doesn't mean your ebuild should inherit it.
Fixed. Thanks! There is an experimental gui that needs gtk+ and webkit. It is now enabled via USE="gui". With USE="-gui" gtk+ is not necessary.