classed/xfce: Make download tarball extention type configurable

Default is still tar.bz2, but there is now option to use tar.xz which is
some of new xfce component releases are only xz compressed tarballs.

Signed-off-by: Khem Raj <raj.khem@gmail.com>

meta-xfce/classes/xfce-panel-plugin.bbclass

@@ -4,7 +4,7 @@ REQUIRED_DISTRO_FEATURES = "x11"
 
 DEPENDS += "libxfce4ui libxfce4util xfce4-panel"
 
-SRC_URI = "http://archive.xfce.org/src/panel-plugins/${BPN}/${@xfce_verdir("${PV}")}/${BPN}-${PV}.tar.bz2"
+SRC_URI = "http://archive.xfce.org/src/panel-plugins/${BPN}/${@xfce_verdir("${PV}")}/${BPN}-${PV}.tar.${XFCE_COMPRESS_TYPE}"
 
 FILES:${PN} += "${datadir}/xfce4/panel-plugins/"
 FILES:${PN} += "${datadir}/xfce4/panel/plugins/"