Started on Sat Mar 14, 1998 (a bit late)

- Mar 14, 1998 (TS): fixed bug in model.pl: append_matrix
                     implemented modelmonitor.pl
- Mar 15, 1998 (TS): reimplemented proof_printing option
		     created file xray_config.pl
                     renamed defaults.pl into xray.pl
		     added compile time flag: compile_complete_search/0
                     Remark: Backtracking is possible by calling aquery(P,_,...),
				where P is the proof to be backtracked upon.