From: James Morris <jmorris@redhat.com>

This patch against current bk makes the recently added SELinux boot
parameter feature a configurable option, and enables SELinux by default
when selected.  These changes were made following feedback including 
discussion on the SELinux list.

The rationale for the changes is to allow SELinux to be be configured and
enabled unconditionally.  If the boot parameter option is selected, then
SELinux is now enabled unless selinux=0 is specified at the kernel command
line.