Revert getObject Types.OTHER change

PR #40 had some unintentional side affects. Make a more targeted fix by treating `null` type name the same as `unknown` during `getObject()`.

Also fix the `runsingletest` target, which was broken with the source layout shuffling, and add conditionals to IntervalTest to ensure everything is working.

Note: INTERVALs are still returned as Strings because PGInterval does not support parsing our interval string format.