setup.hs uses ProgramSearchPath, not available in Cabal 1.16, but no versioned dependency on newer cabal

[joshtriplett]

HDBC-postgresql uses ProgramSearchPath, not available in older versions of Cabal, but doesn't include an appropriate version constraint. We had Cabal 1.16 installed, which didn't work, but HDBC-postgresql's version constraint allows that version.

/tmp/HDBC-postgresql-2.3.2.4-233794/HDBC-postgresql-2.3.2.4/dist/dist-sandbox-fc3e54a/setup/setup.hs:40:53:
    Not in scope: type constructor or class `ProgramSearchPath'