ext: perfomance note about dnet_ext_list_combine()
defrag: reintoduced missed lock

Lock was lost in 3541f980:
    "Added defragmentation status. Depend on eblob 0.18.3+"
ext: check for supported version
ext: removed useless comment
ext: added packed attribute, just to be sure
backend: blob: remove deprecated functions
backend: blob: remove inpossible cases
backend: blob: remove _timestamp prefix from funcion names