CORE-2121 DB2: DiffChangeLog/GenerateChangeLog/DropAll sees alias column and tries to drop/add them

Remove duplicate foreign key columns
Created 3.4 XSD
Don't include "catalog" differences in object comparisions by default
CORE-2132 Error message for missing sqlFile reference should be more descriptive
CORE-2133 Oracle: GenerateChangeLog of a table with DEFAULT VALUE NULL creates defaultValueComputed="NULL"