detect circularity when constructing an environment

[moodymudskipper]

This will run forever, though it doesn't have to :

env <- new.env()
env$e <- env
construct(env)
We should keep a table of visited environments, and fall back to new.env() when we find circularity.
Maybe this should be done for first release since it's a bad look when nothing happens.

[moodymudskipper]

moved since now default behavior doesn't trigger this

[moodymudskipper]

Rather than have {constructive} keep track of environments I think it would be better to have a function assess if the environment refers to itself