Built-in type-name keywords are currently flagged when used as
identifiers in formats that do not support that type. So if a
user declares a dimension named "string" in a classic .cdl file,
it causes an error.
This PR modifies ncgen to allow those format-specific type keywords
to be used as identifiers when compiling to formats that do not
support that type. Also added a test for this.
Also a couple of misc. changes to conditionalize some debug output.
