- add myplc-devel subpackage

- add myplc-devel subpackage
- Old versions of myplc used to ship with a bootstrapped database and
  /etc/planetlab directory. Including generated files in the manifest
  was dangerous; if /plc/data/var/lib/pgsql/data/base/1/16676 changed
  names from one RPM build to another, it would be rpmsaved and thus
  effectively deleted. Now we do not include these files in the
  manifest. However, to avoid deleting these files in the process of
  upgrading from one of these old versions of myplc, we must back up
  the database and /etc/planetlab and restore them after the old
  version has been uninstalled in %triggerpostun.
- add changelog