Smarter %postun script to preserve /var/rancid on upgrade and removal

Previosly the %postun would delete /var/rancid even when performing
an update. Not good! Now it will move /var/rancid to /var/rancid.rpmsave
and save any existing /var/rancid.rpmsave to /var/rancid.rpmsave.[date].

Update %global commit