xfce4 updates

[Olivier Fourdan]

Hi all,

I've changed autogen.sh script for xfce4, xfwm4 and libxfcegui4 to make
use of env vars for automake, autoconf, aclocal and libtool commands.

This is to avoid using, for example, autoconf-1.6 in the autogen.sh
script because this is quite distribution specific (some distribution
install more than one version of the gnu tools and postfix them using
the version number)

Jasper, I've also modified the panel to make use of the preview
fileslector instead of the basic gtk file selector.

There is also a bug in the panel that place the popup menu in some weird
location when adding new item. I did not investigate any further on
this.

Cheers,
-- 
Olivier               <fourdan at xfce.org>            http://www.xfce.org
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XFce is a lightweight  desktop  environment  for  various *NIX systems. 
Designed for productivity,  it loads  and  executes  applications fast,
while conserving  system resources. XFce is all free software, released
under GNU General Public License.    Available from http://www.xfce.org