Bug fixes, code clean up and minor enhancements

Remove auto-autofs-media-setup: autofs only works well for NFS
auto-check-ports-branch: Handle existing but empty $PORTSDIR
auto-mark-package-critical: Return non-zero if package is not installed to notify caller of potentially critical error
auto-update-system: Record time stamp of successful full upgrade
auto-pkgsrc-setup: Enable relro by default on all platforms except Linux (breaks gcc packages)
Other minor fixes and enhancements