Modules missing in cabal file

[larskuhtz]

When building out of a package tar-ball generated with cabal sdist I get:

Preprocessing executable 'Client' for dns-api-0.2.0.1...

example/Client.hs:40:8:
    Could not find module ‘API’
    Use -v to see a list of the files searched for.
Updating documentation index /Users/lars/Library/Haskell/doc/index.html
cabal: Error: some packages failed to install:
dns-api-0.2.0.1 failed during the building phase. The exception was:
ExitFailure 1