SI-3971 error message carat mispoints at curried methods.

Point at the beginning of the first argument list when
reporting an error, as this is most easily associated with
the application taking place (which may involve multiple
applies in succession.)

Thanks to retronym for figuring out why issuing a better
error message broke the compiler on non-erroneous compile runs.
The changes to "treesInResult" are the consequence.
Merge pull request #2996 from paulp/pr/3971

SI-3971 error message carat mispoints at curried methods.