tibbles and classed columns

[moodymudskipper]

depending on how tidyverse/tibble#1541 turns out we might define these as corrupted, though it doesn't seem right since the tibble() call sometimes works if the right namespace is loaded.

We can't know which namespace to know from the object alone though, and if the class is important enough (as sf's probably are) we might have constructors for those and mitigate the issues for this class.

[moodymudskipper]

We view it as corrupted