'RELENG_7_0_0_RELEASE'.

This commit was manufactured to restore the state of the 7.0-RELEASE image.

Inherit setting of the default emulation version to the jails.

Pointed out by:	jhb
Submitted by:	rdivacky

No need to lock prison in a case of linux_use26 because the int
setting is atomic and process cannot leave jail.

Submitted by:	kib
Reviewed by:	jhb
Requested by:	rdivacky

  Redo the checking for 2.6 emulation. We now cache the value of
  use26 and replace calls to linux_get_osrelease() + parsing with
  a call to linux_use26(). Typical path is lockless now.

  Pointed out by: kib

This allows to ship RELENG_7_0 with a default osrelease of 2.4.2 and the
possibility to enable 2.6.x emulation without the possible performance
impact of the previous version of the check.

Submitted by:	rdivacky

Broken by:	netchild

Pointyhat to:	netchild

which existed to cleanup the linux_osname mutex.  Now that MTX_SYSINIT()
has grown a SYSUNINIT to destroy mutexes on unload, the extra destroy here
was redundant and resulted in panics in debug kernels.

MFC after:	1 week
Reported by:	Goran Gajic ggajic at afrodita dot rcub dot bg dot ac dot yu

Submitted by:	Jung-uk Kim <jkim@niksun.com>

Use positive, not negative logic.

on AMD64, and the general case where the emulated platform has different
size pointers than we use natively:
- declare certain structure members as l_uintptr_t and use the new PTRIN
  and PTROUT macros to convert to and from native pointers.
- declare some structures __packed on amd64 when the layout would differ
  from that used on i386.
- include <machine/../linux32/linux.h> instead of <machine/../linux/linux.h>
  if compiling with COMPAT_LINUX32. This will need to be revisited before
  32-bit and 64-bit Linux emulation support can coexist in the same kernel.
- other small scattered changes.

This should be a no-op on i386 and Alpha.