Allow init to execute shutdown

In many inittabs, there's a line like
"ca:12345:ctrlaltdel:/sbin/shutdown -h now" which triggers a shutdown or
a reboot on Ctrl+Alt+Del.
Allow xdm_t to transition to shutdown_t domain

Several DMs offer the possibility to shutdown the system. I personally
don't think a bool is neccessary for this permission, but I wouldn't
oppose one either.
Module version bump for shutdown transitions from Luis Ressel.
Fix misspelling

Fix misspelling using  http://github.com/lyda/misspell-check

Signed-off-by: Elia Pinto <gitter.spiros@gmail.com>
Remove firstboot_rw_t as FC5 has been gone for a long time.
Module version bump for firstboot_rw_t alias removal.