Fix permissions on local_auth.db

I commited a change that made the nipapd.postinst script set the
permissions on the local_auth.db file to 0640 and ownership to
root:nipap. This works fine on a system just running nipapd but on a
system which also hosts the web UI it will break things as the web UI
needs to be able to read the local_auth.db file as well. The web UI is
typically run by apache2 which in turn runs as www-data and subsequently
does not have read access to local_auth.db. I want to add that I did try
my changes on the nipap-demo but due to my login being cached I didn't
run into this problem.

Long term fix would probably be to implement #207. Fix for now is merely
to allow everyone to read the file again.
Fix pid file issues in init script

The pid file resides in /var/run/nipap but as /var/run is symlinked to
/run which in turn is a tmpfs, the /var/run/nipap directory is not
retained through reboots.

Previously the postinst script was responsible for creating the
/var/run/nipap directory but as we need to do this at least on every
boot, the functionality has now been moved to the nipapd init script. In
addition some of the functions have been made more robust to handle the
lack of a /var/run/nipap directory.

Last but not least, the postinst script now starts nipapd at the end of
the installation!
Version 0.20.2

Fix for the nipapd init and postinst scripts related to the pid file!