Linux 3.11 compatibility fix

As of Linux 3.11, v4l2_dev must be present for video_register_device to succeed.
trying to keep pre-2.6.29 compatibility

the v4l2_dev required since linux-3.11 has been introduced in linux-2.6.29.
since we officially still (try to) support kernel's down to 2.6.29,
we need some helper functions for these oldish kernels.

but really, we should start dropping support for old kernels.
Released 0.7.1