% value = tk_dialog(title, text, bitmap, default, ...)
%
% open a dialog window named 'title' with 'text' printed and N buttons
% named as the optional arguments, with button numbered 'default' being
% the default action. The return value is the number of the clicked button.
% First button is number 0.
%
% eg: ret = tk_dialog('Warning', 'You are about to erase the whole disk. Are
% you sure?', 'questhead', 0, 'No','Yes', 'Have I asked you something?')
% will return 0 if the first button (No) is clicked, etc.
%
% there are 6 meaningfull bitmap names: error, hourglass, info, questhead,
% question and warning. All arguments must be strings, except 'default'.