When I say

cabal install --with-ghc=/home/simonpj/5builds/HEAD-2/inplace/bin/ghc-stage2

I get this

ghc-stage2: ghc no longer supports single-file style package databases (dist/package.conf.inplace) use 'ghc-pkg init' to create the database with the correct format.

Now, this is an old build tree, and I could blow it away entirely, but maybe there is something else going on.  What should I do?

Thanks (all on Linux)

Simon