Effects:
Equivalent to
function(read_Βsymlink(existing_Βsymlink), new_Βsymlink) or
function(read_Βsymlink(existing_Βsymlink, ec), new_Βsymlink, ec), respectively,
where in each case function is create_Βsymlink or
create_Βdirectory_Βsymlink as appropriate.