To inspect the state of the application it is useful to checkout the
directory content of the temporary working directory. Setting the DEBUG
variable to either 1 or true stops bootstrap.sh to delete that directory,
which it does regardless if the app finished successfully or because of
an error.
Having to clone from github or a remote repository in general during
development is a waste of bandwidth, time and does not work during
development while a change is being tested and not yet commited or
pushed. Now remote urls can be configured through two env variables:
MACOS_SYSTEM_REPO_URL and ZSHLIB_REPO_URL.
