Increment version number in anticipation of a firmware hex push.

ArduPlane/ArduPlane.pde

 /// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
 
-#define THISFIRMWARE "ArduPlane V2.27"
+#define THISFIRMWARE "ArduPlane V2.28"
 /*
 Authors:    Doug Weibel, Jose Julio, Jordi Munoz, Jason Short, Andrew Tridgell, Randy Mackay, Pat Hickey, John Arne Birkeland, Olivier Adler
 Thanks to:  Chris Anderson, Michael Oborne, Paul Mather, Bill Premerlani, James Cohen, JB from rotorFX, Automatik, Fefenin, Peter Meister, Remzibi, Yury Smirnov, Sandro Benigno, Max Levine, Roberto Navoni, Lorenz Meier