Copy stable/11@r303970 to releng/11.0 as part of the 11.0-RELEASE
cycle.

Prune svn:mergeinfo from the new branch, and rename it to RC1.

Update __FreeBSD_version.

Use the quarterly branch for the default FreeBSD.conf pkg(8) repo and
the dvd1.iso packages population.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Remove misc NULL checks after M_WAITOK allocations.

MFC after: 1 month
Sponsored by: The FreeBSD Foundation

xen: import a proper event channel user-space device

The user-space event channel device is used by applications to receive
and send event channel interrupts. This device is based on the Linux
evtchn device.

Sponsored by: Citrix Systems R&D

xen/evtchn/evtchn_dev.c:
- Remove the old event channel device, which was already disabled in
the build system.

dev/xen/evtchn/evtchn_dev.c:
- Import a new event channel device based on the one present in
Linux.
- This device allows the following operations:
- Bind VIRQ event channels (ioctl).
- Bind regular event channels (ioctl).
- Create and bind new event channels (ioctl).
- Unbind event channels (ioctl).
- Send notifications to event channels (ioctl).
- Reset the device shared memory ring (ioctl).
- Unmask event channels (write).
- Receive event channel upcalls (read).
- The new code is MP safe, and can be used concurrently.

conf/files:
- Add the new device to the build system.