Revert "SELinux: do not handle seclabel as a special flag"

This reverts commit 308ab70c465d97cf7e3168961dfd365535de21a6.

It breaks my FC6 test box.  /dev/pts is not mounted.  dmesg says

SELinux: mount invalid.  Same superblock, different security settings
for (dev devpts, type devpts)

Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Eric Paris <eparis@redhat.com>