Revert "packagesdb.py: log with facility info in load_packages_urls()."

This reverts commit b703c54ac35c331b4e2034961915fd1a60daa78c.
open_packages_url: switch to urllib2 and add error handling

Signed-off-by: Andreas Beckmann <anbe@debian.org>
open_packages_url: try .gz if .bz2 is not available

Signed-off-by: Andreas Beckmann <anbe@debian.org>
update special cases for experimental

currently nothing is needed

Signed-off-by: Andreas Beckmann <anbe@debian.org>