Massaged altroot handling to avoid on-stack struct nameidata instance (and
got it faster, actually).  We are in the middle of do_follow_link() recursion
here, so the stack footprint is critical.
Signed-off-by: Al Viro <viro@parcelfarce.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>