Fix error message in case of unknown criterion value

When failing to parse a criterion rule, the pfw was outputing: `Value error:`
This did not help to find the root cause.

With this patch it would have output:
`Value error: <Input value> is not part of criterion <Criterion>`
(Of course replacing <*> by the apropriate value)
Are you sure `strError` is always useless in this context?

I agree that the new error message is far better than the old one, but I am unsure that the `strError` is always useless in this case.
Maybe we should check all the calls to `CSelectionCriterionRule::parse()` to ensure `strError` is always empty/not relevant here