Minor cleanup to brick size calculation with overlaps.
Minor cleanup to brick size calculation with overlaps.

Splits the calculation out to a separate method, which also now
handles the casting required to avoid win32 warnings.

git-svn-id: 353be9ac11a1e711854a13efcc2fc17d9d6b83e7@1092 c36c8488-0289-0348-9b64-b301f74bd9a7

BlueBrain/Tuvok,BlueBrain/Tuvok,BlueBrain/Tuvok