do not autorelease build ids when a child of mysql-test-run.pl dies

mysql-test/lib/mtr_unique.pl

@@ -10,11 +10,17 @@ use Fcntl ':flock';
 # Requested IDs are stored in a hash and released upon END.
 #
 my %mtr_unique_assigned_ids = ();
+my $mtr_unique_pid;
+BEGIN {
+	$mtr_unique_pid = $$ unless defined $mtr_unique_pid;
+}
 END { 
+	if($mtr_unique_pid == $$) {
 		while(my ($id,$file) = each(%mtr_unique_assigned_ids)) {
 			print "Autoreleasing $file:$id\n";
 			mtr_release_unique_id($file, $id);
 		}
+	}
 }
 
 #