[9fans] change for libthread/ioproc.c

[Fco.J.Ballesteros <nemo@plan9.escet.urjc.es>]

Hi,

	when you create an ioproc and later interrupt it with iointerrupt,
(since there's no handler set) the xioproc process dies. This means that
the process performing the iocall hangs forever waiting in the receive from
the ioproc channel.

I think that xioproc() could add this near its begin:

	threadnotify(ionoted, 1);

with

	static int
	ionoted(void*, char* n)
	{
		return (strcmp(n, "interrupt") == 0);
	}


The result is that iointerrupt interrupts the current io operation which then
returns -1 with the `interrupted' status.

If there's anything else I'm missing and the current code should work
correctly I'd be happy to know it (I already changed our libthread).

hth