[PATCH v10 0/2 hurd] Add irqhelp library and clean up ddekit

[Damien Zammit]

Hi,

This patchset adds a new library irqhelp for assisting the attachment
of irq handlers in userspace.

The previous problem was that return(NULL) was crashing netdde while 
pthread_exit(NULL) works for exiting the irq thread cleanly.

The mach_msg_server thread now shuts down cleanly by setting the
irq->port to a dead name outside of the irq handler thread, thus
not requiring a new interrupt to be triggered to shut the thread down.

TESTED: by compiling netdde.static and trying ifdown/ifup a few times
and transferring a large file from the vm.

Thanks,
Damien