[Chimera-users] hide dust

[weimin wu]

Sometimes after we remove the dust using the tool of hiding dust, we
want to save the map directly instead of using command "mask #0 #0" to
generate a maskfile. The reason is that the masked map has minimized
map size and different with original one. Even after we recover the
map size and origin, it always has half pixel issue, and if we apply
this mask to original map, the output will have some masking artifact.
The iso-surface of the output will not be as smooth as original map or
the map after hiding dust.

weimin