[Pkg-haskell-maintainers] Bug#590514: haskell-pretty-show: FTBFS: missing build dependency on happy

[Aaron M. Ucko]

Package: haskell-pretty-show
Version: 1.1.1-1
Severity: serious
Justification: fails to build from source

Automatic builds of haskell-pretty-show have been failing with the
error

hlibrary.setup: The program happy is required but it could not be found

Please add a build dependency on happy and check that no others are
missing.

Thanks!