Fixed bug in do_boolean() where while loops were using a deleted shell to iterate to the next shell in the shell list. Also some slight rearrangement (for clarity) in the (operation == BOOL_Subtraction) if statement.
Fixed bug in do_boolean() where while loops were using a deleted shell
to iterate to the next shell in the shell list. Also some slight
rearrangement (for clarity) in the (operation == BOOL_Subtraction) if
statement.

cutplane/cutplane,cutplane/cutplane