(PUP-3364) Improve the error message for numeric resource titles

This improves the error message when a numeric resource title is
used in a resource reference, or when a numeric attribute name is
referenced. The message used to be too generic, and used internal
Ruby types instead of puppet types in the message string.
Merge branch 'pr/3136' into stable

* pr/3136:
  (PUP-3364) Improve the error message for numeric resource titles