[RFC PATCH 00/14] libxl: Asynchronous event cancellation

[Ian Jackson <ian.jackson@eu.citrix.com>]

Comments on my approach would be very welcome at this stage.
This applies only on top of my async suspend series.

I have compiled it but I HAVE NOT EXECUTED IT.

There is nothing to exercise this.  I think it might be possible to
make xl have a SIGINT handler which DTRT, but only at the cost of
making it multithreaded or giving it its own event loop.

Preparatory work on the suspend code's dodgy error handling:
 01/14 libxl: suspend: switch_logdirty_done takes rc
 02/14 libxl: suspend: common suspend callbacks take rc
 03/14 libxl: suspend: Return correct error from callbacks

Switching to libxl__xswait* to reduce number of timeout call sites:
 04/14 libxl: Use libxl__xswait* in libxl__ao_device
 05/14 libxl: xswait/devstate: Move xswait to before devstate
 06/14 libxl: devstate: Use libxl__xswait*

Public API changes:
 07/14 libxl: New error codes CANCELLED etc.
 09/14 libxl: domain create: Do not destroy on cancellation
 13/14 libxl: ao: Cancellation API

Internal API changes:
 08/14 libxl: events: Permit timeouts to signal cancellation
 10/14 libxl: ao: Record ultimate parent of a nested ao
 11/14 libxl: ao: Count the nested progeny of an ao
 12/14 libxl: ao: Provide manip_refcnt

Actual functionality!
 14/14 libxl: ao: Timeouts are cancellable