Add position to PostgresException message

[NinoFloris]

This adds a lot of value for tracking down dynamic sql errors as exceptions are usually logged with just the message.

[roji]

See #2151 for a more complete discussion around this (may be a dup).

[NinoFloris]

Ah thanks, yeah multiline with even more info is fine too. I believe automapper and some ioc libraries have exceptions like this, so it's not that uncommon

[roji]

@NinoFloris interested in doing this?