Debian's which hunt

My issue with it lies more in completion and thought process when writing it than anything else. The `old` argument is relative to the `new` final location. But I must write `old` before I have written where `new` is (or write the command's arguments in reverse order). Of course, if `old` is absolute or `new` lacks a `/`, it all works out just fine, but when it doesn't, I have to stop and remember that tab completion is going to lead me astray with `old`.