Usually the backup created by the first deployment is used for a clean
file to make further deployments from, but when the game is updated,
that is reversed, as now the original file is newer than the backup.
In such a case, we first copy the new file to our backup before
continuing with the deployment.
The current implementation is not fool-proof (e.g. it'll do weird stuff
if users mess with the files manually) and doesn't cover everything. But
it should be enough for the regular use case.
Closes#90.
