FlightGear - Flight Simulator FGAddon

This follows from the proposal at
http://thread.gmane.org/gmane.games.flightgear.devel/77385 and the discussions
at http://thread.gmane.org/gmane.games.flightgear.devel/77270.

The changed files have the extensions '*.ac', '*.bak', '*.eff', '*.jpg',
'*.nas', '*.png', '*.rgb', '*.txt', '*.wav', '*.xml'. These are clearly not
executable files. The svn:executable repository property has therefore been
removed so that these files are no longer executable on GNU/Linux and Mac OS X
systems.

The aircraft affected by this change are: 707, 777, A380, F-35B, Harrier-GR1,
ju52, Lockheed1049h, MiG-21bis, PC-21, PC-9M, rah-66, Su-25, T-50,
Vickers-Vanguard, Yak-130.