MFC r259609 (by se):
Fix overflow for timeout values of more than 68 years, which is the maximum
covered by sbintime (LONG_MAX seconds).

MFC r259633 (by se):
Fix compilation on 32 bit architectures and use INT64_MAX instead of
LONG_MAX for the upper bound check.
MFC r268843 (by bapt):
Extend kqueue's EVFILT_TIMER by adding precision unit flags support.
MFC r271315 (by joel):
Minor mdoc nit.

MFC r275806:
Markup fixes for kqueue(2), no content changes.
MFC r275401: zfs_putpages: actually update mtime and ctime