Screen/dc1394: Basler SFF feature support.

Allow optional use of some SFF "SmartFeatureFramework" features of
Basler cameras:

- CRC checks on frames to detect corrupted video frames especially
  reliably. Very time consuming: + 10 msecs for 640x480 images on a
  fast machine.

- Capture timestamps from the camera, computed from firewire bus
  timestamps to tag start of image exposure. Doesn't work with the
  two tested models of Basler cams though - they report a constant
  and totally bogus value! Code audit of our code and libdc1394 and
  comparison with Basler's spec doesn't show any bugs. Mystery...

- Framecounter values from camera. Only workable if the camera allows
  power-cycling by us, so we can reset the counter to a well defined
  zero value at camera open time. One Basler cam allows this, the other
  doesn't allow power-cycle, so this feature causes hard hangs!

- Improved 'GetCycleCounter' query: Now maps count to seconds of bus
  time. The firewire bus has a clock tick of ~24 Mhz so resolves time
  in ~1/24th microseconds. Due to only a 32-Bit counter the timestamps
  wrap around every 128 seconds though, so special remapping and
  wraparound handling is needed to make use of this feature.

- Minor fixes here and there, some refactoring.

-> Screen for 64-Bit Octave on Linux rebuilt and tested.
-> VideoMultiCameraCaptureDemo contains demo code, but mostly commented
   out, as only the CRC checking proved to be consistently working on
   tested cameras.