1401 - shave 80% off chessboard test time

It was all going to laboriously writing out 300+ MB to disk.

027debug.cc

@@ -46,6 +46,19 @@ case _STOP_TRACING: {
   break;
 }
 
+:(before "End Primitive Recipe Declarations")
+_CLOSE_TRACE,
+:(before "End Primitive Recipe Numbers")
+Recipe_number["$close-trace"] = _CLOSE_TRACE;
+:(before "End Primitive Recipe Implementations")
+case _CLOSE_TRACE: {
+  if (Trace_stream) {
+    delete Trace_stream;
+    Trace_stream = NULL;
+  }
+  break;
+}
+
 :(before "End Primitive Recipe Declarations")
 _EXIT,
 :(before "End Primitive Recipe Numbers")

050scenario.cc

@@ -116,7 +116,7 @@ void run_mu_scenario(const scenario& s) {
     setup();
   }
   run("recipe "+s.name+" [ " + s.to_run + " ]");
-  if (not_already_inside_test) {
+  if (not_already_inside_test && Trace_stream) {
     teardown();
     ofstream fout((Trace_dir+Trace_file).c_str());
     fout << Trace_stream->readable_contents("");

chessboard.mu

@@ -26,6 +26,7 @@ recipe main [
 # program.
 
 scenario print-board-and-read-move [
+  $close-trace  # this test generates a 300+ MB trace!
   # we'll make the screen really wide because the program currently prints out a long line
   assume-screen 120:literal/width, 20:literal/height
   # initialize keyboard to type in a move