QUICKFIX: Calendar display buglet when translated

The archive module calendar indexes the array used to build up the header cells by the short names of the days. In Hungary, we have both Wednesday and Sunday start with the same two letters, so if I translate the short versions with the same two letters, the second associative array index will overwrite the first. The obvious soluion was to swap the array, and index by the full day name, which is expected to be unique in all languages. Patch attached.

Note that this applies to 4.5.x and CVS too.