EMI: Implement screenshot thumbnails for savegames
GRAPHICS: Initialize/Destroy _storedDisplay
EMI: Free materials as soon as they are no longer in use by any costumes.
Merge pull request #954 from chkr-private/savegame-screenshots

EMI: Implement screenshot thumbnails for savegames
Merge pull request #967 from Akz-/emi-fix-savecrash

EMI: Free materials as soon as they are no longer in use by any costumes