cancel_query via direct access to the exec_id of the running query process;

retain original messages properties, e.g. for retrieval via Command.Results;

clarified toplevel_error: absorb and print interrupts; tuned;

more explicit error;

tuned message;

removed unused YXML_Find_Theorems and Legacy_XML_Syntax;

more robust read_query; avoid pointless position, which is always line 1 for single-line input;

removed commented out declaration

tuned

merged