added build support for Ubuntu 8.04

let Bareos build on Ubuntu 8.04.
However, QT-based programs (BAT, traymonitor) and Python plugins will not be build.
Note: also not part of Ubuntu 8.04, debhelper >= 7.0.50 is required for building.

Signed-off-by: Marco van Wieringen <marco.van.wieringen@bareos.com>
Rebuild configure.
Some changes to make clean target.