Report boxed math warning on function that boxes primitive return value
With the new :warn-on-boxed (CLJ-1325), these examples do not report a boxed math warning although they each do boxing:
Cause: emitBoxReturn has a hard-coded call to box a prim return value.
Solution: If *unchecked-math* is set to :warn-on-boxed, emit a warning on boxing of primitive numeric return types.
Attached patch does the job, but from trying it out on some real code, it finds both problematic cases and lots of cases that could safely be ignored and/or where there is no obvious way to fix the warning. I think it may need some more tuning to reduce the rate of unfixable things a bit.