Added Failing Test for Overridden Fields

Simply mapping any table with any overridden field causes the tests to fail, at least with the postgres dialect.  This commit adds a struct with an overridden field and maps it to cause the tests to fail.
Fixed Overridden Fields

With this commit, any embedded structs with fields that are overridden in the base struct will have their fields overridden in the dbmap, too, so that the column isn't used twice in database queries.