Asserts with side effects

[Buristan]

A quick grep inside our codebase found several places where assert has side effects (due to typos in them, I suppose).

grep -n -A1 'assert([^=]*[^!<>=~]=$' -R src/
src/box/sql/build.c:3664:       assert(sql_session_opts[id - SESSION_SETTING_SQL_BEGIN].field_type =
src/box/sql/build.c-3665-              FIELD_TYPE_STRING);

grep 'assert(.*[^!<>=~]=[^=]' -R src/
src/box/lua/net_box.c:  assert(transport->self_ref = LUA_NOREF);
src/box/xrow_update_bar.c:      assert(op->opcode == '='); # it's OK

IINM, @mkokryashkin has some ideas about preventing this from happening in the future.