Merge remote-tracking branch 'origin/1.7' into 1.8

src/box/alter.cc

src/box/engine.h

src/box/key_def.cc

src/box/key_def.h

src/box/memtx_engine.cc

src/box/memtx_engine.h

src/box/space.cc

src/box/sysview_engine.cc

src/box/sysview_engine.h

src/box/vinyl.c

src/box/vinyl_engine.cc

src/box/vinyl_engine.h

test/box/alter.result

test/box/alter.test.lua

test/box/ddl.result

test/box/ddl.test.lua