SCI: Provide more accurate error messages for unsupported saved games
SCI: Skip some still unsupported robot files in RAMA
SCI: Some minor cleanup
SCI: Allow saving without a VERSION file in Jones

Apparently, the original does the same. Fixes bug #6535
SCI: Fix NS rect calculation in GK1 (and SCI32 in general)

This fixes the regressions caused by refactoring in SCI32. Thanks to
Timo Korvola for tracking down the issue and providing an initial
patch in bug #6452
SCI: Adapt the segment and offset getters/setters for SCI3

This is by no means complete, but it's a good start. It is based on an
earlier discussion on the subject, and it allows us to use the highest
two bits from the segment for offset addresses