support for active_start_index and active_end_index, for distributed, also bugfix: order of adding virtual columns and the validation
support for active_start_index and active_end_index, for distributed, also bugfix: order of adding virtual columns and the validation

maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex,maartenbreddels/vaex