Add tests for behaviour changes in 0.21.2
Add tests for behaviour changes in 0.21.2

* Unreachable code is now detected within closures that are unreachable themselves.
* Same for uninitialized accesses.

xpol/luacheck,xpol/luacheck,mpeterv/luacheck,xpol/luacheck,mpeterv/luacheck,mpeterv/luacheck