Rename various *Verbose fields to *Verbosity instead

Despite appearances this is actually not completely pointless.
For the Cabal-1.4 branch we need the *Verbose fields to have the
same types as they did in Cabal-1.2, becuase lots of Setup.hs
scripts use them and our change to make them all have type Flag
makes many Setup.hs scripts fail. A solution for the 1.4 branch
is to rename the real field and to add the old field back in.
To keep as much similarity as possible between the HEAD and 1.4
branches I'm applying the name change in both.
On the plus side it's a better name anyway.