Remove BSD4 from Cabal.Distribution.License.License

[igloo]

I doubt any Haskell software actually uses the BSD4 license, and it is likely to confuse users as it looks like a newer version of BSD3.

Currently we have

data License = ... | BSD3 | BSD4

so I propose moving to one of

data License = ... | BSD3
data License = ... | BSD
data License = ... | BSD3   | OldBSD
data License = ... | BSD    | OldBSD
data License = ... | NewBSD | OldBSD

( http://www.opensource.org/licenses/alphabetical lists it as "New BSD license")

All but the first will require changing a number of packages. We could leave the old BSD3 name as deprecated for a while, though.

[duncan]

We may also want to add some other common licenses, eg MIT and perhaps also support licenses with version numbers, ie (L)GPL.

[duncan]

For example of probably confusion see:  http://hackage.haskell.org/cgi-bin/hackage-scripts/package/hbeat-0.1

The LICENSE file included in that package seems to be BSD3.

[duncan]

We cannot actually remove it immediately but it is now on the way to being deprecated because sdist and hackage now warn about its use.