Fix require

We don't seem to use sx-filter anywhere in here
Use correct method

`sx-request-make' wouldn't behave correctly on this
Ensure error string can print

"%s" must take a string, but what we get might not be string-y.
Merge branch 'sx-question-mode' of github.com:vermiculus/stack-mode into sx-question-mode

I neglected to pull before I started committing.