Merge branch '170427' of github.com:jwpi/util-linux

* '170427' of github.com:jwpi/util-linux:
  hwclock: remove unused stdarg.h
  Docs: update howto-usage-function.txt
  hwclock: add --update-drift check
  hwclock: slice up the usage text
  hwclock: update --help content and grammar
  hwclock: use RTC in help output
  include: update pathnames.h
  hwclock: add usage() functions heading
  hwclock: update usage() FILE name
  hwclock: update usage() to util-linux style
  hwclock: remove dead code in usage()