LP bug#683507: xtrabackup should be updated to use the latest 5.1, 5.5 and XtraDB releases
Updated xtrabackup's Makefile and the 5.5 patch so that they are now based on MySQL 5.5.7.
In addition, to simplify maintenance the parallel transfer functionality was changed to use os_mutex_* API rather than the mutex_* one because the last one was changed in 5.5.