Increase the rate at which we increase detail and put a limit on the LOD
multiplier so that it never takes more than about five seconds to return to
default detail.  Also, since there seems to be a weird issue where OS X
throttles the frame rate to 30 fps (independent of our own throttling), use
that as the lower adjustment range.
Merge pull request #2603 from ey6es/master

Increase the rate at which we increase detail and put a limit on the LOD