Stage SELinux config file in the sysroot.

This is needed to build policy modules outside of the refpolicy.
Policy module build systems need to determine the name of the policy
that will be in effect on the target host. This allows them to
locate the policy headers that will be under
$sysroot/usr/share/selinux/$name/include. Given that there *could*
be more than one policy installed in the sysroot we can't assume
that the policy installed there is the only policy to build against.
Add recipe to build example policy module.
Add bbappend for 3.10 kernel.
Add sysvinit to DISTRO_FEATURES in oe-selinux distro.

The oe-selinux distro won't build against the master branch of
oe-core unless sysvinit is in DISTRO_FEATURES.
Commit c72ec4b52827f75351790eab483d258b2e87611a in oe-core adds a
sanity check to the packagegroup class that requires the
VIRTUAL-RUNTIME_init_manager explicitly be set in DISTRO_FEATURES.