This script should be in the root of the git repo so that the config in
Jenkins' web interface is always just:
./jenkins-build
This commit also includes a little code to make it easier for people to run
this script on their own machines, if they want to reproduce the Jenkins
build setup.
This now figures out the root of the fdroidclient project and works there,
rather than just working in the root on the project. So it can be run like
./tools/zip-build.sh or (cd tools && ./zip-build.sh) or whatever.
I also removed the pointless function, since it is only called once in the
script.
