Improve for loop error

[DavidKnott]

- What I did

Improve for loop error message. @khotkevych is is this error clearer?
Fixes #562

- How I did it

Looked at what caused the error and changed the error message to match it.

- How to verify it

Look at the error I changed.

- Description for the changelog

None

- Cute Animal Picture

[fubuloubu]

I think @khotkevych's example actually still satisfies what the error message says, but it doesn't compile (and I don't think it should). The error message should probably say something more like "range only accepts positive, non-zero integers as arguments"

[DavidKnott]

@fubuloubu It does satisfy the error message but the error that triggers the ones I changed is only when the number of iterations isn't fixed as different errors are triggered when num_iterations <= 0.

[fubuloubu]

Ah, maybe something like "range only accepts literal values"

[jacqueswww]

+1 for "range only accepts literal values"

[DavidKnott]

Changed it to "range only accepts literal values," merging it in.