Consistently say Debian $VERSION_NUMBER ($CODENAME).

And:

 * don't specify the point-release number that is (".0"), since it's currently
   wrong, and would be hard to keep up-to-date;
 * don't mention that Wheezy is the current Debian stable, since IMO that's
   not important enough to warrant mentioning and keeping up-to-date (it's
   going to be wrong in 3 weeks).

Closes: #9086