Fix error parsing for foreign key constraints

I checked the docs and looks like the error has been "on table <table> violates foreign key constraint <constraint>" since postgres 7.4
http://www.postgresql.org/docs/7.4/static/tutorial-fk.html
http://www.postgresql.org/docs/9.3/static/tutorial-fk.html

I tried to run the tests, but ran into problems getting things set up cleanly on OSX