Creation of app bundle with icon file for Mac OSX in RELEASE mode

Works with (replace ... by the Drawpile source directory):
cmake ... -DRELEASE=ON -DCMAKE_INSTALL_PREFIX=./release
make install
Then the app is on ./release/bin/

Bundled and tested on OSX 10.6.8 x86_64, network connection tested with another computer with OSX 10.8.2.