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)

Add proper const keywords to sysctl(3) parameters.

The `name' and `newp' arguments can be marked const, because the buffers
they refer to are never changed. While there, perform some other
cleanups:

- Remove K&R from sysctl.c.
- Implement sysctlbyname() using sysctlnametomib() to prevent
duplication of an undocumented kernel interface.
- Fix some whitespace nits.

It seems the prototypes are now in sync with NetBSD as well.

#include <string.h> for strlen()'s prototype.

Fix SCM ID's.

Suppress compiler warning by adding a type cast.

Add the function sysctlnametomib to libc. Details on the semantics
and use of this function have been added to the sysctl.3 manual page.