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)

Minor changes from Berkeley DB 1.86 and further improvements from OpenBSD.
This does not include the new hash routines since they will cause problems
when reading old hash files.

Since mpool(3) has been changed, provide a compatibility shim for older
binaries.

Obtained from: OpenBSD

Use C comments since we now preprocess these files with CPP.

Add symbol maps and initial symbol version definitions to libc.

Reviewed by: davidxu