Add a move to trash menu option (Bug 10980)

This adds a "move to trash" menu option to better match Thunar's
menu. Since there's a trash option now, the delete option always
deletes the file.
Add runtime debug support

This patch adds the ability to enable and disable debug messages
for xfdesktop while it is running. It also converts most of the
DBG messages to XF_DEBUG ones except where it would cause a lot
of noise. Additionally, when built with --enable-debug=full the
XF_DEBUG messages will be on by default. The point of this patch
is to allow the users to easily provide more details in their bug
reports.
I18n: Update translation fr (100%).

217 translated messages.

Transifex (https://www.transifex.com/projects/p/xfce/).