bug#10489: 24.0.92; dired-do-copy may create infinite directory hierarchy

[Stefan Monnier]

>> There's a crucial line missing between the above two.  It should clearly
>> document what this function is expected to do.  E.g. it should make it
>> clear if (and if so, to what extent) the function is allowed to refer to
>> the actual file system(s) as opposed to only relying on the
>> provided strings.
> If the file name strings are not obviously equal, `file-truename' will

I don't mean "document what the code currently does" but "document
what the code should do".

>   "Return non-nil if NAME1 and NAME2 refer to the same file in the file 
> system.
> If either name is not absolute, then it is expanded relative to
> DIR (if given) or `default-directory' for the test."

That description is too vague: an implementation based on comparing
file-attributes would seem to fit, whereas it's clearly not the semantic
we want to provide.


        Stefan