Merge pull request #26 from euroelessar/master

Added signal blockers per threads
Elliptics version update: 2.21.2.2
Updated leveldb backend config
Get rid of smack backend in favour of leveldb
If leveldb doesn't return data, set error to -ENOENT to match others
elliptics-dev/dbg must depend on elliptics with the same version
Sync error codes used in other backends. Enable bulk read. Return -ERANGE if user provided offset, it is not used in leveldb
Elliptics version update: 2.21.3.0
prepare_latest_callback() should break after it found entry in sorted array with dnet_id->group_id and swapped it with the first one
array_result_holder should return vector of templated types, not ints
Fixed statistics behaviour in cpp module