By now, the package was trying to overwrite "/etc/banner" in the image,
which caused opkg to stop the operation, as this file is already
provided by the base-files package. Without the --force-overwrite option
set for opkg (e.g. in the global gluon Makefile, where it is not set by
default), the installation of the package will fail.
Hence the problem got circumvented by renaming the customized banner file
provided by this package to "/etc/banner.ffpb" and using the prerm,
preinst, and postinst hooks of the packages' make-file to rename the
already existent "/etc/banner" to "/etc/banner.openwrt" and establish a
symbolic link "/etc/banner" to "/etc/banner.ffpb".
For deinstallation of the package, this link gets removed and a new one
(pointing at "/etc/banner.openwrt") gets created.

First of all, the ffpb-debug script is now written in lua and thus requires
a lua interpreter to be installed. But since the script makes use of some
gluon-specific lua-functions/-variables (such 'site_conf' in site_conf.lua),
we have to make ffpb-debug depend on the 'gluon-core', which in turn would
define all other dependencies.
Moreover, since ffpb-debug-live got rewritten to work with Barrier Breaker
(i.e. gluon 2014.4 and later), the already defined dependency towards the
busybox package does not suffice any longer, as we fetch interface-details
and -statistics via ubus now. As ubus outputs its data in JSON, we moreover
need the helper functions from the 'libubox' package for a convenient hand-
ling of such data in shell scripts.