Add xorg.conf_SeparateScreensIntel as a sample xorg.conf for Dual-X-Screen.
Screen/GStreamer: Whitespace/Indentation cleanup for video capture.

Prep work for real changes.

-> Screen for 64-Bit Octave on Linux rebuilt.
Screen/GStreamer: Improve diagnostics for videocapture - print more info.

Not very useful for practical purpose though. Anyway, the work is
done so keep it in case it is ever needed.

-> Screen for 64-Bit Octave rebuilt and tested.
Screen/GStreamer: Fix memory leaks when video capturing to memory.

If video is "recorded" to memory instead of immediately
dequeuing, processing and discarding frames, e.g., as in
VideoOfflineCaptureDemo, then severe memory leaks can happen.

This is partially our fault, and this commit fixes the found
leak inducers.

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

However, for certain use patterns, GStreamers - or more
accurately GLib's - default memory slice allocator seems
to misbehave and cause large leakage of memory anyway. It
eventually frees memory, but only at certain trigger-points,
which depending on the machines memory configuration may be
too little, too late.

Testing with the environment variable setting...

export G_SLICE=always-malloc

... can switch to a more simple malloc() memory allocator
which frees "freed" memory immediately via the OS malloc
implementation, instead of caching "freed" memory chunks
in a SLAB allocator or per thread magazine allocator.

While this has a performance penalty, it seems to reliably
prevent memory leaks.

-> This is mostly only needed for "offline capture" into
memory, not for regular live capture->process->display->discard
operation.