V4L2 file handles and event interface

Hi,

Here's the eighth version of the V4L2 file handle and event interface
patchset.

The patchset has been tested with the OMAP 3 ISP driver. Patches for
OMAP 3 ISP are not part of this patchset but are available in Gitorious
(branch is called event):

	git://gitorious.org/omap3camera/mainline.git event

The patchset I'm posting now is against the v4l-dvb tree instead of
linux-omap. The omap3camera tree thus has a slightly different
version of these patches due to different baselines.

Some more comments from Hans and Laurent. What has changed:

- Improved documentation.
- V4L2_EVENT_ALL only valid in unsubscribing.
- Events are initialised in v4l2_fh_init() if
video_device->ioctl_ops->vidioc_subscribe_event is defined.
- Event ioctl handlers are called in __video_do_ioctl() iff
video_device->ioctl_ops->vidioc_subscribe_event is defined, no other
constraints.
- Blocking operation for VIDIOC_DQEVENT.
- v4l2_event_subscribe_many() is gone.
- Fixed memory leak in v4l2_event_subscribe()

Comments are welcome as always.

Cheers,

-- 
Sakari Ailus
sakari.ailus@maxwell.research.nokia.com