When we give a msg about failing to parse a variable, we should say what the variable was, and ideally what was wrong with it. Compare the results for running `./src/app/tor UseBridges 99` in 0.3.5 and in master. With 0.3.5 you got: `Boolean 'UseBridges 99' expects 0 or 1.` but now you get `Unrecognized value 99.` Let's make that better.