File and line numbers in error messages

[Greg Hudson]

On Wed, 2009-04-29 at 15:28 -0400, Sam Hartman wrote:
> Note that krb5_set_error_message is a public API (so it can be used in
> plugins) so you don't want to change its calling semantics or turn it
> into a macro.  I'd also argue that it would be bad if code built with
> this flag had a different ABI in terms of accessor or public exports
> than code built without this flag.

What are the pitfalls here?  If necessary, I can introduce a new
internal interface and use it in the libraries.

I wasn't going to conditionalize the back-end support.