added support for generateChangelog on DB2iSeries

[thomseno]

added DB2 for IBM i catalog tables to support sequences and unique contraints

[blankser]

LOL, I've made the exact same changes and was about to commit them.
I actually made some more changes:
-/liquibase/sqlgenerator/core/FindForeignKeyConstraintsGeneratorDB2.java has some queries that are incompatable with DB2i. However, it seems that this is not used. Am I correct?

• I noticed a problem with generating foreign keys. Some (well in my case most) of them aren't picked up. This is because the CatalogAndSchema object is filled with the db2 instance name as catalog, and the schema name as schema name.
  any way I modified DB2iDatabase as such to resolve it (also to ignore system views):

   @Override
    public String getJdbcSchemaName(CatalogAndSchema schema) {
        return schema.getSchemaName()!=null?schema.getSchemaName():schema.getCatalogName();
    }
    @Override
    public boolean isSystemObject(DatabaseObject example) {
        if (example == null) {
            return false;
        }

        if (example instanceof View && example.getName().startsWith("SYS")) {
            return true;
        }
        return false;
    }

[nvoxland]

Merged changes into master for the 3.1.0 release. @blankser you are right that FindForeignKeyConstraintsGeneratorDB2 isn't used for DB2i, only for DB2.

I've made changes to how the foreign key detection works, can you try a new build from master and see if it is working better?