Penrose: Multi-target Writeback

Penrose supports Mult-target Writeback where a single LDAP operation against Penrose server would be translated to many write operations to the backend stores (multitarget). If all back-end stores are XA-aware, Penrose can execute XA-write back (for example, System 1 and System 2 must update, or the entire transaction rolls back). This feature is quite useful for provisioning multiple accounts.