gl texture additions and reinitialisation, and v4l file descriptor accessor

Signed-off-by: Richard Newcombe <r.a.newcombe@gmail.com>
Merge branch 'devel' of github.com:stevenlovegrove/Pangolin into devel
Merge branch 'devel' of github.com:stevenlovegrove/Pangolin into devel
fixed openni 2.1 header for Linux

Signed-off-by: Richard Newcombe <r.a.newcombe@gmail.com>