Update notes for submitted changes

* ext4: speed up truncate/unlink by not using bforget() unless needed Do not iterate over data blocks scanning for bh's to forget as they're never exist. This improves time taken by unlink / truncate syscall. Tested by continuously truncating file that is being written by dd. Another test is rm -rf of linux tree while tar unpacks it. With ordered data mode condition unlikely(!tbh) was always met in ext4_free_blocks. With journal data mode tbh was found only few times, so optimisation is also possible.