Warn about experimental nature of dual board

The message field, which for now is unused, now contains a warning message.
Make switching between board windows absolute

Selecting the window in which to draw the board when the slave board for
-dualBoard was up was done by a toggle. For unknown reason this could cause
a situation where the drawing took place in the other window than the
intended one. The code is made more robust by explicitly specifying which
window to draw in, based on the partnerUp flag.
Remove checkbox for 'Move Sound'

This function is better controlled from the Sounds dialog.
Don't add PV moves on board clicking in AnalyzeMode

Playing PV moves by right-clicking the PV was only intended for clicks
in the engine Output window, selecting from multi-PV analysis output,
where by default it plays only the first move. PV walkig by right-clicking
the board, however, would start the walk at the end even in AnalyzeMode,
and thus add the entire PV. Which is probably not useful. So adding moves
in that case has now completely been suppressed, so it can be used for
harmless viewing of the latest PV.
 The behavior has also been made subject to a persistent Boolean option
-appendPV, configured to true, with a checkbox in General Options.
 A checkbox has also been added there for controlling the -variations option,
which is now also configured to true.
Add new vertical pixel fudge

With the new GTK window type the board is 13 pixels too small.
Allow display of 50-move counter in zippy mode

No chance it could be considered cheating there.
Add -onlyOwnGames option

This suppresses auto-saving of ICS observed games.
in debug mode also print the git-version if available during build
add keyboard shortcuts back into Xaw version