Comment 4 for bug 567629

There was discussion about this on ubuntu-devel several years ago: https://lists.ubuntu.com/archives/ubuntu-devel/2007-March/023332.html

I don't know that it was ever codified in policy, but the Vcs-* fields aren't codified in Debian Policy either (they're part of the Developer's Reference: http://www.debian.org/doc/manuals/developers-reference/best-pkging-practices.html#bpp-vcs)