Follow r275792 eliminating fdt_data_verify().
Add a facility for non-init process to declare itself the reaper of
the orphaned descendants.  Base of the API is modelled after the same
feature from the DragonFlyBSD.

Requested by:	bapt
Reviewed by:	jilles (previous version)
Tested by:	pho
Sponsored by:	The FreeBSD Foundation
MFC after:	3 weeks
Fix typo.
Remove empty generated file upon gperf failure

Prior to this change the build could fail as follows, if gperf is not
available (or fails):

  - make(1) stops due to the gperf error, but an empty target file
    (cfns.h) is still created
  - the empty cfns.h is newer than the source cfns.gperf so it is not
    regenerated on subsequent builds
  - the gcc build fails (undefined reference to libc_name_p)

Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Fix incorrect type of "invalids" argument in __iconv() prototype.
Markup fixes for kqueue(2), no content changes.

Reviewed by:	brueffer (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	3 days