Merge branch 'dmesg-subsecond' of https://github.com/t-8ch/util-linux

* 'dmesg-subsecond' of https://github.com/t-8ch/util-linux:
  dmesg: use subsecond granularity in iso format
  dmesg: add subsecond granularity for --since and --until
  lib/monotonic: get_suspended_time: use usec_t
  timeutils: add utilities for usec_t conversions
  dmesg: add test for --since and --until