Why: MR !389 changed the signature of PDB procedures to return GStrv instead of (int, GimpStringArray)
This changes handling of results from a call to such a changed signature, in a Scheme script.
The symptom was a cryptic TinyScheme "Error: car: argument 1 must be : pair"
Most changed procedures are named like "-list".
I did a cursory grep to look for other instances.
Updated porting guide doc.
