* make sure exit after reset.
* more wide guardian range. We should trap reset_on_interrupt as soon as
we are about to change any files.
* check INITIAL_BRANCH against UPSTREAM_BRANCH
* use HOMEBREW_REPOSITORY instead of HOMEBREW_PREFIX
* better performance:
* update-bash: avoid shellout
* update-report: use strip_prefix and tr
* more robust:
* explicitly handle the case when repo is HOMEBREW_REPOSITORY to avoid
to handle the trailing backslash.
* handle both lower case and upper case when stripping non alpha and
digital characters.