[barcode] Patch for barcode border

[Markus Berg]

Allesandro wrote:
>
> So please ping me back on friday, as by then I'll surely have
> forgotten the barcode queue.

Hello Allesandro, I'm pinging you back as requested. 

I've refactored my patches to extend the backend as well as the frontend
(see attachments). Also, this version of the second patch (borders
around barcodes) doesn't break pcl output.

Single barcode-per-page printing are unaffected by these patches.
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best regards
Markus Berg