MFC r335280-r335281, r335302: sysrc.subr updates

r335280: Fix handling of files with missing newline at EOF
r335302: Fix a comment for accuracy

PR: bin/203435
Reported by: Andreas Sommer <andreas.sommer87@googlemail.com>

r335281: Fix display when value is "-n"

PR: bin/226406
Reported by: Marius Halden <marius.halden@modirum.com>

Sponsored by: Smule, Inc.