backends: more robust dnet_ext_hdr_*()
it: minor cleanups
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
ext: eblob: remove deprecated functions
ext: eblob: remove inpossible cases
ext: eblob: remove _timestamp prefix from funcion names
it: minimize number of asserts in library
codespell: grammar nazzi
test: fix append test
ext: blob: fix append of existing record
test: add simple cas test
ext: eblob: fixed checksum calculation for extended records
Merge pull request #75 from SaveTheRbtz/master

Extended format fixes. Append and CAS.