[barcode] Patch for barcode border

[Markus Berg]

Hello,

attached is a patch for optionally printing a thin border around
barcodes in table mode. The patch adds a "-B" command line switch which
causes a thin (0.1pt) gray border to be printed outside the barcode and
padding. This is useful when printing a grid of labels which you'll
later be cutting up into individual labels.

It's an extension of my previous patch (Improved layout control when
printing tables).
---
best regards
Markus Berg