every use of BSD4 on hackage is incorrect

[Felix Martini]

Right now i cannot see a reason why the cabal license field is an
enumeration instead of a string. The purpose seems to be to direct
people to preferred licenses of the Haskell community. If so this is
the wrong approach imo. A good explanation of licensing on the
haskell.org wiki is better. Btw. the Haddock headers in the GHC source
code also use custom strings for the license field.

Felix