undo, save
Set the maximum number of past configurations that can be saved in memory, 
using the 
undo and 
save mechanisms. Everytime this number 
is exceeded, the oldest configuration is discarded forever.
Although the number of 
undo and 
save levels 
does not affect performance, the memory required to handle 
multiple windows, with multiple layers, each layer with 
undo and 
save past configurations in memory,
can be significant. Therefore, 
undo and 
save
parameters should be kept to relatively low values, particularly
undo, where new configurations are generated automatically,
without any user intervention. 
save works exactly as 
undo,
except that configurations are saved manually by users.
Example: <layer undo="5" save="5"/> (default)
(defined in GAMGI_ENGINE_UNDO and  GAMGI_ENGINE_SAVE)
Allowed values: non-negative integer (optional)