Add examples and/or a test suite

[lpsmith]

Especially with the 0.9 release, there have been a few reports of link errors due to attempting to use libpq 8.4 or libpq on Windows. Given that postgresql-libpq will successfully compile against the libpq 8.4 headers, but won't link with the libpq 8.4 object code, a minimal test suite would be useful as a smoke-test for linkage errors. Some guidance for dealing with common problems would also be useful.

Perhaps Setup.hs should check the version of libpq as well.