cabal no longer supports package version tags

[guest]

The following cabal file below triggers an assertion fail on the second install:

$ cabal --version
cabal-install version 0.13.3
using version 1.13.3 of the Cabal library

$ cabal install
Resolving dependencies...
Configuring foobar-0.2.0...
Building foobar-0.2.0...
Preprocessing library foobar-0.2.0...
[1 of 1] Compiling FooBar           ( FooBar.hs, dist/build/FooBar.o )
[1 of 1] Compiling FooBar           ( FooBar.hs, dist/build/FooBar.p_o )
Registering foobar-0.2.0...
Installing library in /home/hvr/.cabal/lib/foobar-0.2.0/ghc-7.2.2
Registering foobar-0.2.0...

$ cabal install
Resolving dependencies...
Configuring foobar-0.2.0...
cabal: Distribution/Simple/PackageIndex.hs:123:8-13: Assertion failed

Only when I unregister the installed package via ghc-pkg unregister foobar I can configure the package again...

The cabal file causing this behaviour:

name:                foobar
version:             0.2.0-git20111120
synopsis:            none
license:             BSD3
license-file:        LICENSE
author:              foo
maintainer:          foo@bar
build-type:          Simple
cabal-version:       >=1.10

library
  default-language: Haskell2010
  exposed-modules: FooBar
  build-depends: base

The FooBar module is just a dummy empty module. This used to work previously, e.g. with

$ cabal-0.11.2  --version
cabal-install version 0.11.2
using version 1.12.0 of the Cabal library

[duncan]

Package version tags are no longer supported. We should make this explicit and fail up front with a better error message.