Improve stty handling in it2check and it2getvar

[elyscape]

This copies the more robust handling of stty from it2ul to it2check and it2getvar. Trapping the stty restoration on EXIT means we're covered in all situations that might cause the script to exit early, not just the user hitting Ctrl+C, and means we don't need to remember to do it in the script's happy path. Accordingly, this fixes an issue in which it2getvar did not restore the stty settings if execution completed without issue.

[gnachman]

Thanks!

[elyscape]

@gnachman Any idea when you'll have this and #51 rolled out to the website?

[gnachman]

As soon as a new beta goes out. I should do that this weekend

[elyscape]

Sounds good. Thanks!