Catch this invalid use case.
Fix several autoincrementKey issues.

- Changing a column to autoincrementKey failed if it already contained values.
- The trigger and sequence weren't created when adding an autoincrementKey
  column via addColumn().
Fix using addColumn() with autoincrementKey types in SQLite.
Add autoincrement unit tests.
Add a migration test.
[jan] Fix migration with Oracle.