* if config.tmp_dir is not writeable defaults to /tmp/pisi-$USER
* if /var/cache/pisi/archives is not writeable defaults to /tmp/pisi-$USER
* Move chowning additional files into postinstall
* Assume that group == owner if no group is given for AdditionalFiles
BUGS:
All files extracted under work_dir and installed under install_dir
has owner:group == uid:gid of the user which builds the package.
TEST:
Build a package with your regular user and install it
EXPECTED RESULTS:
You shouldn't have any exceptions but the files installed on your
system will have the same ownership as your user ;)