Backend for DB2 9
=================

Modified management.py to use a get_max_constraint_length from the backend if available.
Reason: DB2 has a 18 character limit on constraint names, although table_names may be 128 characters.

Added to settings:
- DATABASE_SCHEMA: use this to have inspectdb find only tables from a specific schema, NOT NEEDED for normal operation.
- TEST_DATABASE_USER  must be an existing user (DB9 uses OS authentication)
- TEST_DATABASE_PASSWORD
- DATABASE_CHARSET: I use this to encode the data to and from the database (I needed iso-8859-1 compliance for legacy db)



Issues:
- Deferral of foreign key constraint checking : DB2 does not know this ? 
    ? Option: do a "SET INTEGRITY FOR X OFF READ ACCESS CASCADE DEFERRED" 
    and a "SET INTEGRITY FOR X IMMEDIATE CHECKED" at commit ?
    COULD NOT GET THIS TO WORK YET 
- flushing also fails due to this limitation --> alike solution ?
- no regex lookups
- order of objects.all() --> test needs improving (default ordering)?

- new forms custom date/time cleaning is failing on me why ?

- character sets


Googling for TRUNCATE:
    On Unix :
        db2 connect to <dbname>
        db2 import from /dev/null of del replace into <table-name>
    On Windows:
        Create a blank file C:\temp\blank.txt
        db2 connect to <dbname>
        db2 import from C:\temp\blank.txt of del replace into <tablename>
or
    ALTER TABLE T ACTIVATE NOT LOGGED INITIALLY WITH EMPTY TABLE;
    COMMIT;