[gnu.utils.bug] diff of file and directory should only use last component of path

gnu@toad.com (10/11/88)

Unix diff can do things like:

	diff file dir
or
	diff dir file

and it will diff "file" against "dir/file".  GNU diff does this too,
but it takes the "dir/file" literally.  Unix diff actually just uses
the last component of the filename, e.g.

	diff /usr/include/stdio.h .

will diff "/usr/include/stdio.h" against "./stdio.h".  GNU diff compares
"/usr/include/stdio.h" against ".//usr/include/stdio.h".