Added new paxos client connector for fibers
Fixed vacuum/snapshot performance issues

Vacuum is now ran in parallel with disk sync and retrieves only records
that need to be vacuumed by iid, without full scan of the state using
linked list. Now works faster and more reliable.

Snapshot writing has been desynchronized using random delay, since it
has a performance hit when ran synchronously on all nodes.
Added bytes written to stats logging
Fixed mutex lock/unlock asymmetry

It lead to unlock for a mutex not owned by current fiber, which
resulted in assert failure later in libevfibers.
Added validating assertions for mutex calls
Squashed 'evfibers/' changes from d17d37d..1ff4825

1ff4825 Merge pull request #5 from miihael/master
9fa5cd4 fix 'undefined reference to symbol floor@@GLIBC' when linking tests

git-subtree-dir: evfibers
git-subtree-split: 1ff48255d4f48b21ae5727000617fc3bab6d953f
Merge commit '1cf60c3ac6a7ef3b04aa149d93d5a94f5b13a4f8' into paxos-connector
Dropped acceptor truncate margin option
Fixed mutex usage in client fiber
Added noreclaim block in paxos value sending
Fixed undefined mctx in client

Luckily it did not affect anything as mctx is unused in fbr_mutex_init.

Also tweaked the logging a bit.
Fixed the connector

Now it does not hang in case the connection to the cluster (and within
a cluster) is poor.
Fixed latency calculation
Added an utility to dump the WAL/snapshot file
Fixed ballot numbers to be actually 64bit

They were encoded using msgpack_pack_unsigned_int, which resulted in
loss of data bits. Also used 64bit encoding for all other 64bit values.
Fixed strings_client behavior

Now it calculates "late" values and tries to resubmit values timed out.
Fixed uuid size in ffi.cdef
Added service_id and best_before header fields

best_before is currently unused.
Fixed calculation of lowest available upon restore
Fixed payload start offset in dump