Allow the installer to install packages and remain in the temp dir

The installer will look in the directory 'packages' for a file named 'package-list.txt'. This file contains the names of all package installation xml files which should be installed.

The package installation xml files are ant script which must reside in the packages directory. The installer will call the 'install' target defined in each package installation xml file.

Unsupported: by specifying an extra parameter on the command line the created temp directory will no be removed afterwards.