Merge remote-tracking branch 'origin/master' into 1.6

src/box/box.cc

src/box/lua/schema.lua

src/box/memtx_engine.cc

src/box/recovery.cc

src/box/recovery.h

src/box/replication.cc

src/box/replication.h

src/box/sophia_engine.cc

src/box/vclock.c

src/box/vclock.h

src/box/xlog.cc

src/box/xlog.h

src/fiber.cc

test/box/misc.result

test/replication/once.result

test/replication/once.test.lua

test/unit/fiber.result

test/unit/vclock.cc

test/xlog/errinj.result

test/xlog/errinj.test.lua