Don't forcibly render layer components that are not currently visible; added a mechanism for layer components that know they will never be "under-rendered" to avoid the expense of forced rendering on every tick.
Don't forcibly render layer components that are not currently visible; added a
mechanism for layer components that know they will never be "under-rendered" to
avoid the expense of forced rendering on every tick.


git-svn-id: a1a4b28b82a3276cc491891159dd9963a0a72fae@3805 542714f4-19e9-0310-aa3c-eee0fc999fb1

threerings/narya,threerings/narya,threerings/narya,threerings/narya,threerings/narya