davem says that copy_mount_options is failing in obscure ways if the
architecture's copy_from_user() doesn't return an exact count of the number of
uncopied bytes.

Fixing that up in each architecture is a pain - it involves falling back to
byte-at-a-time copies.

It's simple to open-code this in namespace.c.  If we find other places in the
kernel which care about this we can promote this to a global function.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>