Handle import with LDAP enabled

Import with duplicate users in Hibernate and LDAP will fail if LDAP is enabled when importing

1. bamboo export with duplicated users (same username in ldap and hibernate) works without problems
2. import with ldap enabled of above export causes an error

   2009-09-01 12:08:53,172 INFO [4236043@qtp-3658896-2] [XmlMigrator] Using com.atlassian.bamboo.migration.ServerIDMapper to import.
   2009-09-01 12:08:53,180 INFO [4236043@qtp-3658896-2] [XmlMigrator] Using com.atlassian.bamboo.migration.UserMapper to import.
   2009-09-01 12:08:53,228 ERROR [4236043@qtp-3658896-2] [ImportExportManagerImpl] Exception occurred during import
   com.atlassian.core.exception.InfrastructureException: com.atlassian.user.impl.DuplicateEntityException: User [ukuhnhardt] already exists in AD Repository
   at com.atlassian.bamboo.user.BambooUserManagerImpl.injectUser(BambooUserManagerImpl.java:472)

3. import without ldap enabled of above export runs through - however
   • group memeberships of external users are not maintained and lost.
   • global permissions for external groups are lost

Bamboo should not export duplicated users or handle user duplication during import