#4 DB2 Special: new dialect 'db2zos' for DB2 ZOS

[P.Burri]

I have her some add.ons and some modification for dbmaintain:
- Support DROP and CREATE for databasetype which does not support CREATE OR REPLACE ( e.g. DB2 for ZOS)
Ignoer SQLCODE -204 on DROP STatement

Changed in Module: DefaultSQLHandler.java

- for DB2: while creating Triggers/StoredProcs which calls Stored Procedures in same schema, the path must be set:
after set schema add following statements:
set current sqlid
set current schema
set current path
Module: DB2Database.java and DB2SCriptRunner.java
- New dialect 'db2zos' implemented

- some catalogue queries for db2 sequences modified

[P.Burri]