Screen: Add multi-camera sync support to dc1394 video capture - Part I

This is the control code for starting and stopping synchronous
capture + setup code in 'SetVideocaptureParameter' for selecting
master/slave role and sync strategy.

We allow:

a) Software sync: Start/Stop on a best-effort software basis.
b) Firewire bus sync via broadcast of iso on/off signals from master.
c) Hardware sync via trigger cable.

For c) the setup code for trigger source/mode/polarity is still
missing - tbd.

-> Tested for basic function, but sync precision testing is tbd.
-> VideoMultiCameraCaptureDemo updated to allow multicam sync testing.
-> Screen for Octave on Linux rebuilt and tested.

This is part I of sync support.