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)

Back out last revision that unnecessarily changed valid assembler
line comments and damaged the CVS history.

Prompted by: bde, jhb

After talking to Bruce Evans and reading more standards specs,
switch to using C99-style comments everywhere in preprocessed
assembler. The reason is that lines starting with the regexp
'^[[:space:]]#' are treated as preprocessing directives, and
while it seems to work now with GCC, it's not necessarily has
to work. Use C99 comments `//' for the trailing comments to
save whitespace.

Fix a bug in the AMD64 trampoline. I misunderstood the implicit
32->64 bit zero extend. This changes a movl to an orq.

Approved by: re (amd64 bits)

Enable the i386 loader to load and run an amd64 kernel. If this puts
things over floppy size limits, I can exclude it for release builds or
something like that. Most of the changes are to get the load_elf.c file
into a seperate elf32_ or elf64_ namespace so that you can have two
ELF loaders present at once. Note that for 64 bit kernels, it actually
starts up the kernel already in 64 bit mode with paging enabled. This
is really easy because we have a known minimum feature set.

Of note is that for amd64, we have to pass in the bios int 15 0xe821
memory map because once in long mode, you absolutely cannot make VM86
calls. amd64 does not use 'struct bootinfo' at all. It is a pure loader
metadata startup, just like sparc64 and powerpc. Much of the
infrastructure to support this was adapted from sparc64.