Screen/dc1394: Cleanup of some status messages and of code formatting.

-> white space cleanup in Common/Screen/PsychMovieWritingSupportGStreamer.c
-> Status message updating wrt. video recording vs. GStreamer video processing.
Screen/dc1394: Only report dropped frames if 'dropframes' is true.

Otherwise it just doesn't make lot of sense as a summary at end of capture.

-> Screen for 64-Bit Octave on Linux rebuilt and tested.