Test: Make sure we close all handles

Some VMs (ex. Parrot) don't finalize objects like file handles during
program shutdown, so there may remain data unflushed from userspace.

lib/Test.pm

@@ -29,6 +29,7 @@ my $todo_output    = $*OUT;
 
 try {
     # XXX do this with dup or an analogous cross-platform construct
+    # XXX these should probably have :autoflush
     my $output_h         = open('/dev/stdout', :w);
     my $failure_output_h = open('/dev/stderr', :w);
     my $todo_output_h    = open('/dev/stdout', :w);
@@ -446,6 +447,12 @@ END {
         done;
     }
 
+    for $output, $failure_output, $todo_output -> $handle {
+        next if $handle === ($*ERR|$*OUT);
+
+        $handle.close;
+    }
+
     if $num_of_tests_failed > 0 {
         exit($num_of_tests_failed min 254);
     }