hide/show context managers don't handle exceptions well

[bitprophet]

My understanding of how contextlib.contextmanager works was incorrect -- I thought it handled exceptions, but it doesn't . If an exception occurs during the @contextmanager-using function's yield statement (i.e. inside the with statement using it), the code after the yield won't get run.

This is easily fixed by using try/finally on our end.

EDIT: looks like this actually came up and was fixed for settings() already, as it correctly handles this.