Merge branch 'tuple-update'

include/rope.h

src/box/CMakeLists.txt

src/box/request.cc

src/box/request.h

src/box/tuple.cc

src/box/tuple.h

src/box/tuple_update.cc

src/box/tuple_update.h

src/rope.c

test/unit/rope_common.h

test/unit/rope_stress.c