session: when using send-to-all-backends set backend id via dnet_session_set_direct_backend() call. We can not extend dnet_trans_control because of ABI.
find: set DNET_FLAGS_DIRECT_BACKEND flag which will force client code to set backend ID (session/finer will have direct backend id set to the last backend id from the route table)
backend: moved object size calc (getting into account total size and io->size/io->offset) into common header from eblob. Implemented proper timestamp reading in file backend
state: dnet_state_create() reference counter fix/change

Code comments contain more information about this commit, here is a small note.
dnet_state_create() previously returned state with only one reference being held.
And it could be released by network thread, who actually owns state after it is added into epoll().

But some callers (creating threads) can perform operations on this state, thus it must not be freed
by network thread. dnet_state_create() now returns state with 2 reference being held:
1 for network thread (owner of the state)
2 for caller thread, and caller must release that state after it finished working with it.
Merge branch 'master' of github.com:reverbrain/elliptics