Mention shellcheck

[stuartpb]

http://www.shellcheck.net/ is a linter for Bash that covers a lot of this (and more, too).

repo at https://github.com/koalaman/shellcheck

[relrod]

+1

[cybertk]

+1

[dtruebin]

Mentioned in b00a1a4. Time to resolve the issue?