Bug#758218: live-build: Packages helper includes packages excluded by tasksel

[Daniel Baumann <daniel.baumann@progress-technologies.net>]

applied your patch now as-is; let's think about it (if at all) on how to
do it more 'properly' for when we're in the jessie+1 cycle. it doesn't
make much difference anyway for now and it's more important to just get
it done/working.

thanks, and thanks for the patience :)

-- 
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