Fixing type error in path dialog.

When the directory is bad, we need to send a list of path-labels; the
original code would pass in a path object and would emit a contract
error of the form:

dyoo@kfisler-ra1:~$ set in list-box%: expected argument of type <list of strings (up to 200 characters)>; given ("Bad Directory:" #<path:/home/dyoo/tmp/>)

svn: r9868

collects/mred/private/path-dialog.ss

@@ -321,7 +321,7 @@
                  (send path-list enable #t))
           (begin (set! pnames '())
                  (set! pnames-nulstrings '())
-                 (send path-list set (list "Bad Directory:" dir))
+                 (send path-list set (list "Bad Directory:" (path->string dir)))
                  (send path-list enable #f)))
         (wx:end-busy-cursor))