make menuconfig work for recent xfce environment

xfce terminal was renamed 'Terminal' -> 'xfce4-teminal' mainline end of 2012,
so the distros supporting 'Terminal' will dissapear. The distros not
mentionied in  __init__ do (e.g fedora 19 - tested) fail - or will fail
sooner or later.

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>