Merge branch 'jk/arith-expansion-coding-guidelines'

Merge branch 'jk/arith-expansion-coding-guidelines'

The coding guideline for shell scripts instructed to refer to a
variable with dollar-sign inside arithmetic expansion to work
around a bug in old versions of dash, which is a thing of the past.
Now we are not forbidden from writing $((var+1)).

* jk/arith-expansion-coding-guidelines:
  CodingGuidelines: drop arithmetic expansion advice to use "$x"