uscan: add v prefix in @ANY_VERSION@

This allows uscan to automatically look for upstream version tags like "v1.0.2". Before this patch, one had to manually prefix @ANY_VERSION@ with the letter 'v'.

I often find myself adding a v before @ANY_VERSION@ whenever needed, and I thought that editing the regex in uscan itself might make things easier for everybody.

I did not touch d/changelog, but I added the Gbp-Dch: Full tag in the commit message just in case you use gbp dch. Feel free to edit the changelog as you wish :)

I also tried to update the .po files, hoping that I didn't mess anything up.

Lastly, I'm not really a regex wizard, so please check that this didn't break anything - I tested locally on a few packages, but you can never know.