"usd tag" cannot tag logical tags

When tagging the logical tag, the top of debian/changelog contains the version of old/debian, not of old/ubuntu (since that has been stripped by our workflow). Thus having the tool guess the required version number in the tag is impossible unless it takes more than just the current tree-ish. Our documentation currently says to use it (https://wiki.ubuntu.com/UbuntuDevelopment/Merging/GitWorkflow#Detailed_workflow) so this results in an incorrect logical tag.

We should fix at least the documentation, as right now this makes the workflow completely broken if you follow the docs to the letter.

I'm not sure what to do about fixing "usd tag" itself. We'd need to carry state or something. Or perhaps check against "old/ubuntu" that the trees match (except for debian/changelog and update-maintainer) and then use the version number from the "old/ubuntu" tree instead?

<caribou> rbasak: I may have found the reason : using usd tag on the logical goes to fetch the version in the changelog and, once the changelog is removed from the reconstruct/{vers}, it has the debian version at the top