data-sort: mark all bases for data-sort by default

This will allow us to sort bases that do not exceed theirs' thresholds
even if they are not fragmented.
It's safe because defrag will skip last base of each type anyway.
hash: decrease memory consumption of hash by 10%

Remove now unneeded cache_entry field from hash structure.
On x86_64 this decreses memory consumption of hash control structure
from 112 to 96 bytes.
hash: removed unused declaration
hash: doc: actualize documentation
data-sort: set err on chunk add failure
data-sort: replace assert with if
data-sort: replaced local->current with shortcut.

This makes code more readable.
blob: add atomic comments
data-sort: added sorted file defragmentation note
data-sort: simplify code by removing sort of empty bases
blob: fixed format string warnings
data-sort: remove useless bctl member - need_sorting
blob: use datasort_base_is_sorted API
data-sort: fixed signed/unsigned comparison
data-sort: recheck that old bctl is valid after lock
blob: style fixes
blob: if bctl was invalidated pread would fail anyway
data-sort: we already defragmenting all unsorted bases
blob: set errno on eblob_init failure
hash: remove dead assignment

It's left over from:
    a7e74a7 "hash: remove all disk-caching parts"