Psychtoolbox 3.0.19.8 release "CamJam"

Psychtoolbox 3.0.19 Beta update "CamJam" was released at 14th March 2024.
As usual, the complete development history can be found in our GitHub repository.
The release tag is “3.0.19.8”, with the full tree and commit logs under the URL:

https://github.com/Psychtoolbox-3/Psychtoolbox-3/tree/3.0.19.8

Some of this Psychtoolbox release was sponsored by Mathworks under the year
2023/2024 contract., and our partner SR-Research, makers of the Eyelink gaze trackers.

Compatibility changes wrt. Psychtoolbox 3.0.19.7:

• dontOpenExisting non-zero flag in Eyelink('OpenFile') now error aborts,
  instead of trying to implement something unsupportable.

Highlights:

• None. Mostly a small refinement release.

All:

• Eyelink('OpenFile'): Error out if optional dontOpenExisting flag is set
  to a non-zero value. Update help text. According to feedback from SR-Research
  this is simply not supportable with all current and past Eyelink runtimes and
  tracker host software. Game over for this feature, just warn users about it.

• Gamepad() / Joystick() et al.: Improve docs, help, setup instructions. Especially
  for proper choice of joystick driver on Ubuntu 20.04/22.04-LTS.

• Downloaders/Updaters etc.: Update again for final SVN death on GitHub. In combo
  with website updates, to make clear that functions DownloadPsychtoolbox and
  UpdatePsychtoolbox and DownloadAdditionsForLinux are currently dead.

• SetupPsychtoolbox(): Dead code removal, cleanup, docs updates.

Linux:

• Psychtoolbox was built and lightly tested against Matlab R2023b.

• XOrgConfSelector: Add error handling and error resolution tips.
  There wasn't error handling in case of delete() or copyfile() failure.
  Add something, and try to give some helpful feedback and advice, e.g.,
  running PsychLinuxConfiguration().

• Allow selection of a different clock to be used as the general GetSecs
  clock for (almost) all timing and timestamping, e.g., by GetSecs, WaitSecs,
  PsychPortAudio, Screen, etc. Since the year 2007, the so called wall clock,
  or gettimeofday() clock, or Posix CLOCK_REALTIME clock was used for this,
  and it continues to be the default. But now one can use the new PsychTweak
  function PsychTweak('GetSecsClock', clockid); at the beginning of a
  script (before any other calls to Psychtoolbox mex files!) to select a clock
  with a different clockid. A clockid setting of 0 uses the default CLOCK_REALTIME
  clock, as in the past. A clockid setting of 1 uses CLOCK_MONOTONIC instead.
  CLOCK_MONOTONIC, as opposed to default CLOCK_REALTIME, does not maintain time
  in seconds since 1st January 1970 0:00:00 UTC, but has an unspecified zero
  point, but usually 0 denotes time of operating system boot. CLOCK_MONOTONIC
  is always guaranteed to be monotonically increasing, not subject to step
  adjustments by the system administrator, NTP, PTP, or other external clock
  reference sources. This prevents synchronization to other computer on the
  network/setup, but may avoid clock trouble caused by time jumping in certain
  situations. CLOCK_MONOTONIC behaves like the GetSecs clocks for Psychtoolbox
  on MS-Windows and macOS. For now the new monotonic mode is only lightly
  tested, and only available on Psychtoolbox for Intel processors, not yet for
  RaspberryPi - this will follow in a future release.

  This improvement was sponsored by a Mathworks sponsored support incident under
  our 2023/2024 contract.

Windows:

• Psychtoolbox was built and lightly tested against Matlab R2023b.

macOS:

• Psychtoolbox was built and lightly tested against Matlab R2023b and
  Octave 8.4 from HomeBrew.

• Detect futile attempt of running under native Matlab for Apple Silicon / ARM,
  ie. not under Rosetta2 emulation and bail with more enlightening messages.