clarified Editor.current_command: allow outdated snapshot;
more accurate Document_View.perspective based on current_command for proper state output (see also 88c6e630c15f and ef62204a126b);

 src/Pure

 src/FOL

 src/HOL

 src/ZF

 src/CCL

 src/CTT

 src/Cube

 src/FOLP

 src/LCF

 src/Sequents

 src/Doc

 src/Tools