[CFR] Event channel Interrupts and unified Xen interrupt infrastructure.

[Justin T. Gibbs]

I've been working to get the next chunk of Spectra/Roger Pau Monné Xen work into head.  The latest version of the patch I'm working on can be found here:

	http://people.freebsd.org/~gibbs/xen_intr.diff

I will continue my testing today and commit it tonight unless I hear complaints.  Comments, corrections, improvements, and bug reports welcome.

--
Justin