Comment 1 for bug 1340717

Xtrabackup crashed while tried to delete unused tables. purge_sys if not initialized. Seems to be specific to innodb56. Related parts of code:
trx_sys_init_at_db_start invoked before trx_purge_sys_create:
comment from srv0start.cc:
ib_bh = trx_sys_init_at_db_start();
n_recovered_trx = UT_LIST_GET_LEN(trx_sys->rw_trx_list);
/* The purge system needs to create the purge view and
therefore requires that the trx_sys is inited. */
trx_purge_sys_create(srv_n_purge_threads, ib_bh);
At the same time trx_lists_init_at_db_start invokes trx_resurrect_table_locks, which has been introduced in MySQL 5.6 (revno: 5045). Purpose of trx_resurrect_table_locks to be discovered.