optimize table indexes introspection in DB2
fix table foreign key constraints introspection in DB2
add initial BLOB type support in DB2
fix truncate table SQL in DB2
fix current time, date and timestamp SQL in DB2
add date arithmetic expressions in DB2
fix bit operator expressions in DB2
fix portability connection in DB2
fix default values in DB2
fix renaming columns in DB2
fix autoincrement column introspection in DB2
fix empty to null portability in DB2
fix required table reorganization after table alteration in DB2
add class and object fetch modes support in DB2