better compile-time messages for string functors

[Christian Kamm]

Christian Kamm wrote:
>> In order to avoid showing too much implementation details in the error
>> message, the compiler could make an educated guess about what part of the
>> instantiation chain is of interest to the user. For instance, template
>> instantiations in imported modules could be skipped (if they're
>> private?). I didn't think about that when I added the traces, so LDC
>> currently just prints up to six steps or all if -v is given.

Don wrote:
> Ideally, it would also detect recursive template instantiations -- only
> show (say) the first and the last instantiation of templates with the
> same name. You always want to see the initial template instantiation.

Yep, logic like that may keep the list of instantiations readable.

Anyone interested in improving these error messages in LDC should check out 
this commit:
http://www.dsource.org/projects/ldc/changeset/561%3Ad4e95db0e62b