KeeperRL v1.0 hotfix 6 is out

Squires will retain their special traits after getting promoted to a knight.
Luxury will affect minion training and workshop efficiency.
Retired dungeons will be saved to temporary files and copied after saving is successful to avoid the game crashing on corrupted files.
Luxury of reinforced walls is shown correctly.
Removed irrelevant damage modifier from mushrooms.
Added a tool-tip explaining locked keepers in the keeper menu.
Fixed the [x] button in the keeper choice menu.