Change the inplace package database to not use file-style database.

Instead we use HcPkg.init (e.g. ghc-pkg init). For ghc-pkg this will
create a new directory style db.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>
Signed-off-by: Duncan Coutts <duncan@well-typed.com>
Merge branch 'master' of git://git.haskell.org/packages/Cabal

Edward's patch to stop using old file style package dbs.