2016-04-09 wenzelm 2016-04-09 shared output primitives of physical/virtual Pure;
2016-04-07 wenzelm 2016-04-07 more conventional theory syntax for ML bootstrap, with 'ML_file' instead of 'use'; avoid slowdown of Resources.loaded_files due to command name 'use' in Pure base syntax;
2016-04-06 wenzelm 2016-04-06 virtual thread data via context, for proper support of Context.>> etc;
2016-04-06 wenzelm 2016-04-06 clarified ML bootstrap environment;