[Tilesathome] Render niceness

[David Lynch]

One of the things I've noticed running _unstable on my machine is that
the faster rendering has resulted in optimizing and uploading tiles
being a bottleneck. Stable seems to only run into a situation of the
current render finishing before the previous upload is done when the
rendering is of a blank or very sparse tileset, but eliminating
striped rendering seems to have sped things up enough that optimizing
a tileset where most of the images are non-empty takes longer than the
render of even a somewhat complex tileset.

I know that there's work ongoing to try to improve the speed of the
optimization of tiles, but as a more temporary measure, I've modified
the script on my local machine to use separate niceness values for
rendering and optimizing, and running the optimizing at a higher
priority than the rendering (nice -n5 for optimizing, nice -n10 for
rendering) seems to have sped things up substantially. I can commit
this to SVN if the group is interested, but I wanted to check with
everyone first, especially the server folks, to make sure that the
possible increase in upload frequency wouldn't be a problem.

-- 
David J. Lynch
djlynch at gmail.com