Attach the original Postgres error to unique errors

[kevinburkeshyp]

Currently it gets clobbered, which makes it difficult to determine which
uniqueness constraint failed. This way, you can always check err.originalError
to get the original node-postgres error message, with information about the
constraint, PG error code and table that failed.

[kevinburkeshyp]

Tried to add a test here, balderdashy/waterline-adapter-tests#89, though not sure whether you can write db-specific tests there. I have tests for this in my own code

[kevinburkeshyp]

Looks like this is failing on a different test, I'm not sure why. https://travis-ci.org/balderdashy/sails-postgresql/jobs/75692004#L849

(coincidentally, you can see an example of https://github.com/balderdashy/waterline/issues/1118 in the error message)

[kevinburkeshyp]

just realized if people are using blueprints this may not be the best idea, since it might expose database implementation details to the end user ... ? i don't know exactly how blueprints work.

[dmarcelino]

The changes look good but awkwardly travis build with node 0.11 is breaking, https://travis-ci.org/balderdashy/sails-postgresql/jobs/75692004#L849:

  1) autoIncrement attribute feature should auto generate unique values even when values have been set:
     [Error (E_VALIDATION) 1 attribute is invalid] Invalid attributes sent to undefined:

Not really sure what's going on 😕

[kevinburkeshyp]

Might be a race issue since I just re-ran the tests and they suddenly pass. I'm not sure what's going on; I believe we don't get a full stack trace because an E_VALIDATION error object does not inherit from Error.

We had a bunch of issues with create([array of records]) returning results out of order; I'm not sure if that's an issue here. https://github.com/balderdashy/sails-postgresql/issues/128

[kevinburkeshyp]

Reading through the code in sails-postgresql maybe it's possible it's generating/incrementing ID's in memory? Not super familiar with that code, but that seems like it could be race-y.

Sorry I don't have a huge amount of time to dig into it :(