[sldev] Viewer optimization patch.

[Jason Giglio]

Soft wrote:
> Erf. Results are pretty mixed so far. I'm impressed with how much it
> simplifies the main viewer loop, but I'm not comfortable with the
> degraded avatar effect. ...and maybe it's all in my head, but audio
> seems downright horrible.

I've updated https://jira.secondlife.com/browse/MISC-508 to create a
place to direct all issues with this build.

-Jason