Fix PgsqlAdapter native types, default values.

* The native types array were missing 'real','bigint','smallint', 'double precision', 'decimal' and 'numeric'.  See: http://www.postgresql.org/docs/9.1/static/datatype-numeric.html
* Both 0 and the empty string "" are valid defaults but were not being recognized.  Changed to check explicitly for NULL defaults.
Merge pull request #428 from jpfuentes2/getloaded-pgsql-number-types

Fix PgsqlAdapter native types, default values.