Improving detection of types and auto increment for Postgres.

Since there is some auto magic in Liquibase that creates a sequence for Postgres even though strategy is identity or native we need to treat them as a sequence otherwise they show up in the diff.

The change in heuristics to find the data type improved the comparison between hibernate and Postgres. Hopefully this might help remove the need for the  suppression of differences implemented in the package liquibase.ext.hibernate.diff, but I haven't tested that thoroughly.