[CVE-2010-3086] x86: replace LOCK_PREFIX in futex.h

[Andy Whitcroft]

CVE-2010-3086:

	include/asm-x86/futex.h in the Linux kernel before 2.6.25 does
	not properly implement exception fixup, which allows local users
	to cause a denial of service (panic) via an invalid application
	that triggers a page fault.

It seems that everything Karmic and up already has the fixes required
here.  Hardy has already receieved the fix-up via upstream stable.  The
backport for Dapper seems pretty straight forward.  Following this email
is the backport for Dapper.

Of concern is that I am completely unable to test that this does what it
says on the tin.  This should be identicle to changes in Hardy which
have been in place for a long time; should.

-apw