MFC Xen fixes:

svn rev 250081 Author:gibbs Date:2013-04-29T23:08:13.552620Z
==============
xenstore/xenstore.c:
    Prevent access to invalid memory region when listing an empty
    directory in the XenStore.

Reported by:	Bei Guan

svn rev 250913 Author:gibbs Date:2013-05-22T17:13:03.545339Z
==============
Correct panic on detach of Xen PV network interfaces.

dev/xen/netfront:
    In netif_free(), properly stop the interface and drain any pending
    timers prior to disconnecting from the backend device.

    Remove all media and detach our interface object from the system
    prior to deleting it.

PR:		kern/176471
Submitted by:	Roger Pau Monne <roger.pau@citrix.com>
Reviewed by:	gibbs

svn rev 250917 Author:gibbs Date:2013-05-22T19:22:44.923351Z
==============
Fix loss of the emulated keyboard on Xen PV HVM domains.

xen/xenbus/xenbusb.c:
    In xenbusb_probe_children(), do not modify the XenBus state of
    devices for which we have no PV driver support. An emulated device
    we do support may share this backend.  Hide the node from XenBus
    instead.

    This prevents closing the vkbd device, which Qemu's emulated keyboard
    device is using as the source for keyboard events.

    Tested with qemu-xen-traditional, qemu-xen and qemu stubdomains, all
    working as expected.

Submitted by:	Roger Pau Monne <roger.pau@citrix.com>
Reviewed by:	gibbs
MFC after:	1 week

svn rev 251175 Author:gibbs Date:2013-05-31T04:43:19.944993Z
==============
Apply the ad* => ada* IDE device name transition to the Xen block
front driver.

Submitted by:	Bei Guan <gbtju85@gmail.com>
Reviewed by:	gibbs
MFC after:	1 week

svn rev 251176 Author:gibbs Date:2013-05-31T04:45:59.563195Z
==============
Make netif_free() safe to call on a partially initialized softc.

Sponsored by:	Spectra Logic Corporation
MFC after:	1 week

svn rev 251729 Author:gibbs Date:2013-06-14T03:31:11.033200Z
==============
sys/dev/xen/netfront/netfront.c:
    In netif_free(), call ifmedia_removeall() after ether_ifdetach()
    so that bpf listeners are detached, any link state processing
    is completed, and there is no chance for external reference to media
    information.

Suggested by:	yongari