Commit 3c12a67b added
a dependency on the NFS_SUPER_MAGIC macro, which is
defined in linux/magic.h.  Unfortunately linux/magic.h
is not available in RHEL-5, and causes a compile error.
Just define it locally, since this is something that
can't change.
Signed-off-by: NChris Lalancette <clalance@redhat.com>