Rework of the userspace interrupt handling patch

[Justus Winter]

Hello,

I revised the patch that is delegating interrupts to userspace.
Notable changes:

1/ We now use proper dead-name notifications to detect that the send
right we use to send notifications goes stale, i.e. the userspace
server dies.

2/ 'device_intr_enable' is a nop now...

3/ ... instead the notification message carries a send right as the
reply port, and the userspace server acknowledges the interrupt by
deallocating this right.

This requires a tiny change to libddekit.  I'll send it as a
follow-up.  With it libddekit supports both the new and old kind of
notification to make upgrades painless.

For a step-by-step log how I arrived at the new design, see:
http://darnassus.sceen.net/gitweb/?p=teythoon/gnumach.git;a=shortlog;h=refs/heads/justus/dde-0

WDYT?
Justus