Pure/tctical/suppress_tracing: new; can now switch tracing off until the
next tactical call. There is no good way of doing this because of
backtracking.
Pure/tctical/exec_trace_command,tracify,traced_tac: these set, test and
reset suppress_tracing
#! /bin/csh
grep "$*" {Pure/Syntax,Pure/Thy}/*ML */*ML */ex/*ML