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)

Introduce a new proc service routine ps_linfo() to get LWP info.

Add support for XMM registers in GDB for x86 processors that support
SSE (or its successors).

Reviewed by: marcel, davidxu
MFC After: 2 weeks

Re-implement this file, including copyright notice. Keep David Xu as
copyright owner. Typical bugs fixed by this are:
o various style(9) bugs,
o #ifdef'd out code,
o lack of comments,
o missing const,
o introduction of obsolete functions,
o missing __BEGIN_DECLS & __END_DECLS,

The major flaw in this version, that was also present in the previous
version is the lack of man page. Minor flaws undoubtedly still exist.

Add proc_service.h, the common file both debugger and libthread_db will
use, program wants to load libthread_db.so should provid proc service
interface.