Added first trace implementation
Added trace_id to python bindings.
Merge branch 'master' of github.com:reverbrain/elliptics into trace

Conflicts:
	cache/cache.cpp
Fixed tracing with low log level. Moving trace_id to begin of line in log string.
Traversed trace_id for index requests.
Added trace_id to cache
Renamed back dnet_trace* to dnet_log.
Added trace_id to dnet_backend_log. Added DNET_TRACE_BIT for ignoring current log level for traced request.
Added printing begin and end of id in dnet_dump_id_len
Made elliptics compatible with current eblob version.
Added comments to eblob compatibility solution.
Merge branch 'master' of github.com:reverbrain/elliptics into trace

Conflicts:
	library/pool.c
Merge pull request #217 from shaitan/trace

Added ability to trace request in logs both on client and on server sides.