CI does not work with cabal-install-1.24.0.1

[ezyang]

@hvr updated the cabal-install PPA to 1.24.0.1, but this broke our CI. A representative failure is https://travis-ci.org/haskell/cabal/jobs/175033797

I haven't investigated further.

[23Skidoo]

@ezyang

package-tests: could not build shared Setup executable
  ran: /opt/ghc/7.6.3/bin/ghc-7.6.3 --make -clear-package-db -global-package-db '-package-db=/home/travis/.cabal/store/ghc-7.6.3/package.db' '-package-db=/home/travis/build/haskell/cabal/dist-newstyle/packagedb/ghc-7.6.3' '-package-db=/home/travis/build/haskell/cabal/dist-newstyle/build/cabal-testsuite-1.25.0.0/package.conf.inplace' '-hide-package Cabal' '-package Cabal-1.25.0.0' -O0 Setup.hs
  output:
<command line>: cannot satisfy -package Cabal-1.25.0.0
    (use -v for more information)

IIRC something like this happened before and was fixed by you, but I can't find the ticket right now.

[ezyang]

Reproduced locally; I think this is a redux of #3932. I actually have been working on a rewrite of the test suite which would fix this problem, but it is going to be some more time before I finish it.