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)

The r184588 changed the layout of struct export_args, causing an ABI
breakage for old mount(2) syscall, since most struct <filesystem>_args
embed export_args. The mount(2) is supposed to provide ABI
compatibility for pre-nmount mount(8) binaries, so restore ABI to
pre-r184588.

Requested and reviewed by: bde
MFC after: 2 weeks

Replace the use if ext2fs' bitops by bitstring.h macros. This fixes
portability issues. Also note that for amd64, a hack is used to work
around gcc optimization (thanks to cognet@).

Reviewed by: mux (mentor)
Approved by: re (dougb)

Moving reiserfs from sys/gnu to sys/gnu/fs. This was discussed on arch@.

Reviewed by: mux (mentor)
Approved by: re (scottl)