Made all Boost Jam's ECHO commands automatically flush the standard output to make that output more promptly displayed to the user.

[SVN r46104]

src/engine/builtins.c

@@ -494,6 +494,7 @@ builtin_echo(
 {
 	list_print( lol_get( frame->args, 0 ) );
 	printf( "\n" );
+    fflush( stdout );
 	return L0;
 }