Improve drag-and-drop tests

* lisp/dnd.el (dnd-begin-file-drag, dnd-begin-drag-files): Fix
type of `x-xdnd-username'.
* lisp/select.el (selection-converter-alist): Fix declaration of
_DT_NETFILE converter.

* test/lisp/dnd-tests.el (dnd-tests-verify-selection-data):
Handle "compound" selection converters.
(dnd-tests-parse-tt-netfile): New function.
(dnd-tests-begin-file-drag, dnd-tests-begin-drag-files): Verify
validity of file selection data.

1 files changed, 2 insertions, 2 deletions

diff --git a/lisp/select.el b/lisp/select.el
index 706197e027e..417968b25cb 100644
--- a/lisp/select.el
+++ b/lisp/select.el
@@ -819,8 +819,8 @@ VALUE should be SELECTION's local value."
         (_EMACS_INTERNAL . xselect-convert-to-identity)
         (XmTRANSFER_SUCCESS . xselect-convert-xm-special)
         (XmTRANSFER_FAILURE . xselect-convert-xm-special)
-        (_DT_NETFILE . (xselect-convert-to-dt-netfile
-                        . xselect-dt-netfile-available-p))))
+        (_DT_NETFILE . (xselect-dt-netfile-available-p
+                        . xselect-convert-to-dt-netfile))))
 
 (provide 'select)