Since the unit test is skipped anyway for Oracle, the dropTable() call
should be skipped as well to avoid having a leftover transaction and
cause further transactions to be nested and break the next test suites
requiring transactions.

Added unit test to make sure that checkMigrate() works when adding a
primary key and autoincrement column to a table schema.

adding auto increment/PK to table files_trash

adding PK to table ldap_user_mapping and ldap_group_members

adding PK to table ldap_group_mapping

truncate permissions table to allow smooth creation of primary key

adding unit test for creating an auto increment column on a table which already contains data

remove unneeded table files_trashsizes

fix unit test

no need to truncate *PREFIX*permissions

On Oracle adding auto increment columns is not working out of the box - Oracle migrations are to be done manually

Add a mechanism to try the database migration on a copy of the tables before running it on the "real" data