tell me about pv_ops.

I need to write a blurb about paravirt_ops and what that means for upstream Linux Xen support.  I don't think there are any administrator-visible changes (other than possibly better distro packaging,) but I'm not entirely certain.  (I also have no idea where it'd go, but that's another issue entirely.)

Part of it is just that any term thrown around on the mailing list so much has got to be important, right?  Maybe someone should do a concordance script to find common and significant terms in mailing lists.