Preventing dot "." in keys breaks existing applications.

Consider the large install base of mongo, and the fact many have used it while this was quite "legal" to use a string for a key that contains "." within, I think making it "illegal" is simply wrong, given the fact data current databases with dots in keys are either forced to use old driver, or change keys which nearly impossible.

Given the fact mongo itself, as a database, works just fine with it, it would just sane to make this constrain configurable, letting users decide whether or not their keys will contain a dot.

This is my current code, where this exception raising is commented out in both places.