Mouse xfconf and xfce4-settings improvements

[Nick Schermer]

Brian & Stephan,

I've merged my mouse theme code from the multi_device branch into the
xfce4-settings code. I think it's much cleaner and in some ways better looking
(fully transparent, real theme name nicer preview, better xorg
integration), then
the existing code.

Also made a patch for xfconf to uses g_file_set_contents for better error
reporting and it also run xrdb for cursor theme changes (cursor theme
changes were only written on xft changes).
The patch also fixes a bunch of signed/unsigned and some other compiler
warnings.

Hope it helps,
Nick