Three dubious ways to handle deep indexing

[Dirk Laurie <dirk.laurie@...>]

I want `a.b.c.d.e`. I'm going to test for nil, and I don't care
at what level the missing index is.

1.   x = a and a.b and a.b.c and a.b.c.d and a.b.c.d.e
2.   x = has(a,"b.c.d.e") with
function has(a,idx)
  local j,k = idx:match"([^.]+)%.(.*)"
  if not k then return a[idx]
  else return has(a[j],k)
  end
end
3, debug.setmetatable(nil,{__index=function() return nil end})
x = a.b.c.d.e