Rollback config if syntax check fails. Every resource in a config file.

A syntax check is run before reloading the configuration. If the check
fails, we rollback to the previous Nagios configuration and abort
reloading. Running repeatedly the script won't break your configuration.

For every requested resource, a configuration file is created in
${base-dir}/tmp.d/. If everything is ok, this configuration will be
moved to ${base-dir}/naginator.d/. Otherwise, you keep your old
configuration and the tmp.d/ dir.