rake build on Windows raises a dialog

[frankshearar]

This will break CI builds. The output of rake build up to the point we see the dialog is

$ rake build
C:/Users/frsheara/Documents/git/squeak-ci/Rakefile:17: warning: already initialized constant FU
C:/Users/frsheara/Documents/git/squeak-ci/lib/squeak-ci/build.rb:12: warning: previous definition of FU was here
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target
cp SqueakV41.sources SqueakV46.sources SqueakV50.sources HudsonBuildTools.st C:/Users/frsheara/Documents/git/squeak-ci/target
cp -r C:/Users/frsheara/Documents/git/squeak-ci/target/cog.r3427 C:/Users/frsheara/AppData/Local/Temp/d20160125-14896-1cu9qyw
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target
cp SqueakV41.sources SqueakV46.sources SqueakV50.sources HudsonBuildTools.st C:/Users/frsheara/Documents/git/squeak-ci/target
rm -rf C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak-4.10.2-2612-src-32
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak4.10.2-2612
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak4.10.2-2612
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak4.10.2-2612
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak4.10.2-2612
mkdir -p C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak4.10.2-2612
mv Squeak4.10.2-2612 C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak-4.10.2-2612-src-32
cp -r C:/Users/frsheara/Documents/git/squeak-ci/target/Squeak-4.10.2-2612-src-32/. C:/Users/frsheara/AppData/Local/Temp/d20160125-14896-1964fi6
cp Squeak4.6.image C:/Users/frsheara/Documents/git/squeak-ci/target/TrunkImage.image
cp Squeak4.6.changes C:/Users/frsheara/Documents/git/squeak-ci/target/TrunkImage.changes

It's something to do with assert_interpreter_compatible_image.