Duration of tstheap

[PeterBBBBB]

If the duration argument is not defined at start, the test runs forever. I found for example, running hurd in a VM, there is no response to CTRL-c, so the program cannot be halted without killing the VM

if ( argc >= 2 )
	duration = atoi(argv[1]);

Suggest add an else ( duration = 4000 or whatever).