TRUNK-4936 Fix integration-test on h2 due to liquibase changeset
Some integration-test's failed on h2 due to the introduced liquibase changeset
for TRUNK-4936. ALTER TABLE sql statement generated by h2 contains a
syntax error. h2 does only seem to handle unique constraints well when
creating the table, or on its own and not when adding the column.
* remove the nested <constraints> element from the changeset
* use addColumn and addUniqueConstraint
