A change in Git tag naming

Hi, Since Cabal and cabal-install might not be released at the same time and thus not from the same Git commit we will from now on tag releases in the Git repo as Cabal-vX.Y.Z and cabal-install-vX.Y.Z The "v" in the tag is used to distinguish the tags from branches we might create some time before a release. Such branches would be named e.g. Cabal-1.16. to keep track of what was actually released. -- Johan