use unsigned SIZE type for indexing in all places instead of signed LONGWORD
use UNSIGNED64 for stream size
TODO: UNSIGNED64 has many issues if signed bit(63) = 1 ( detected as HUGEINT )

git-svn-id: https://svn.inf.ethz.ch/svn/lecturers/a2/trunk@8451 8c9fc860-2736-0410-a75d-ab315db34111