Use exact case numbers, to avoid unneeded subtractions.

Files:
modified: /scummvm/trunk/engines/scumm/he/script_v70he.cpp (try)
modified: /scummvm/trunk/engines/scumm/he/script_v90he.cpp (try)
modified: /scummvm/trunk/engines/scumm/he/script_v100he.cpp (try)