* src/workbook-control-gui.c (wbcg_close_if_user_permits): Define
responses GNM_RESPONSE_SAVE_ALL, GNM_RESPONSE_DISCARD_ALL. These
are negative, to work with druid logic in gnumeric_dialog_run.

* src/gui-file.c (gui_wb_view_show): New. Factored out of
gui_file_read. Show  view in a wbcg. Use current or new wbcg
according to policy.
(gui_file_read): Use it.