innobase/include/trx0roll.h:
  Changed prototype of the function trx_rollback_or_clean_all_without_sess
  because this function is executed in a background thread.
innobase/include/trx0trx.h:
  Added support for X/Open XA prepare, recover and search by X/Open XA XID.
innobase/include/trx0undo.h:
  Added support for X/Open XA prepare and recover. We need to store X/Open XA XID
  to the undo log header for recovery.
innobase/log/log0recv.c:
  Create a thread to run trx_rollback_or_clean_all_without_sess function
  to rollback the uncommitted transactions which have no user session.
innobase/row/row0ins.c:
  Remove unnecessary variables.
innobase/trx/trx0roll.c:
  Changed so that trx_rollback_or_clean_all_without_sess is executed
  in a background thread. We should also leave all prepared transactions
  active to wait for commit or abort from MySQL.
innobase/trx/trx0sys.c:
  Only those rows which belong to the active transaction in crash recovery
  are undone.
innobase/trx/trx0trx.c:
  Added support for X/Open XA prepare and recover. We need to store X/Open XA
  XID to trx structure and left prepared transactions to wait for a
  commit or abort from MySQL. This requires also that we add TRX_PREPARED
  state to the transaction and TRX_UNDO_PREPARED state for undo logs.
innobase/trx/trx0undo.c:
  Added support for X/Open XA prepare and recover. We need to store X/Open XA
  XID to undo log header for recovery of distributed transactions.
sql/ha_innodb.h:
  Added prototypes for X/Open XA prepare, recover, commit and rollback.
sql/handler.h:
  Added definition for X/Open XA XID structure.