Add an assert to catch ridiculous brick sizes.
Add an assert to catch ridiculous brick sizes.

I hit this because I forgot a boolean argument to ConvertDataset.
Instead, my brick size argument was taken in boolean context, and
my brick overlap was taken as a max brick size.

Took me forever to track down that the reason I was generating 6
LoDs and 7000 bricks is because I specified a brick size of 4^3.
This assert should guard against future stupidities...

git-svn-id: 353be9ac11a1e711854a13efcc2fc17d9d6b83e7@1397 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok