pkg/sorted/postgres: Renamed "postgresql" -> "postgres" in init()

Change-Id: I8f1ba7c970b57c62741e534c23958918714cee0b
Fixes: Issue 418
Merge "pkg/sorted/postgres: Renamed "postgresql" -> "postgres" in init()"
index: make Postgres test use the JSON constructor.

Would caught camlistore.org/issue/418

Change-Id: Ic323607df355e664d3b76709a7ad56dc40637fcf