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

src/box/field_def.c

src/box/field_def.h

src/box/tuple.h

test/box/access.result

test/box/access_misc.result

test/box/access_misc.test.lua

test/box/alter.result

test/box/alter.test.lua

test/box/net.box.result

test/box/net.box.test.lua