Default desktop files will be installed during compilation time; if this was done during installation
time, files will be installed in superuser directory, which isn't the goal.
Fixed Jamfile to use correct path.
Install ede-xterm.desktop only if Desktop directory is not present or it is empty. This is done by install-in-desktop-dir.sh
script. With this, when EDE is started for the first time, something will be on desktop.