Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

Fix a compiler warning so hash.h can be included in the kernel. This changes
the args for hash32_stre and hash32_strne but there are no consumers in the
base system and openbgpd does not use it which the initial import was for.

Silence on: hackers

Add missing "const" qualifiers.

Submitted by: bde

Revise markup.

Import OpenBSD's manual page to the sys/sys/hash.c functions imported two
days earlier.

Obtained from: OpenBSD