Plane: add Tom Pittenger to developers list

Plane: add Tom Pittenger to developers list. He was added to main Plane.h as "Lead Developer" here *https://github.com/ArduPilot/ardupilot/blob/master/ArduPlane/Plane.h#L2) but never to the main ArduPilot.c file.

ArduPlane/ArduPlane.cpp

@@ -1,7 +1,7 @@
 /*
    Lead developer: Andrew Tridgell
  
-   Authors:    Doug Weibel, Jose Julio, Jordi Munoz, Jason Short, Randy Mackay, Pat Hickey, John Arne Birkeland, Olivier Adler, Amilcar Lucas, Gregory Fletcher, Paul Riseborough, Brandon Jones, Jon Challinger
+   Authors:    Doug Weibel, Jose Julio, Jordi Munoz, Jason Short, Randy Mackay, Pat Hickey, John Arne Birkeland, Olivier Adler, Amilcar Lucas, Gregory Fletcher, Paul Riseborough, Brandon Jones, Jon Challinger, Tom Pittenger
    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, Yury MonZon
 
    Please contribute your ideas! See http://dev.ardupilot.org for details