Added DEFGENERIC form for map-over-extents-at-location*.
Added DEFGENERIC form for map-over-extents-at-location*.

onixie/mcclim,onixie/mcclim,slyrus/mcclim,slyrus/mcclim,onixie/mcclim,swflint/McCLIM,swflint/McCLIM,swflint/McCLIM