Merge branch '1.6' of git+ssh://github.com/tarantool/tarantool into 1.6

CMakeLists.txt

extra/dist/tarantoolctl

src/CMakeLists.txt

src/box/box.cc

src/box/iproto.cc

src/box/lua/schema.lua

src/box/lua/tuple.lua

src/box/memtx_engine.cc

src/lib/salad/bps_tree.h

src/lua/console.lua

src/lua/init.cc

src/lua/strict.lua

src/lua/utils.cc

test/big/lua/utils.lua

test/big/tree_pk.result

test/big/tree_pk.test.lua

test/big/tree_variants.result

test/big/tree_variants.test.lua

test/box/alter.result

test/box/alter.test.lua