git lfs install has a --skip-repo option, which prevents any attempt to
modify the repo if run from within one. Add such an option for git lfs
uninstall as well. Document it and add tests for its functionality.
The printf(1) command, like it's C cousin, takes a format string as its
first argument. If a shell variable is passed as the first argument, it
will be interpreted as a format string; this can lead to surprising
behavior and can cause the test suite to fail if we accidentally insert
a format string character into the variable.
Modify all the places in the individual tests that we use a plain quoted
variable as the format string by running the following Ruby one-liner:
ruby -i -pe '$_.gsub!(/printf "\$/, %q(printf "%s" "$))' t/t-*.sh
Avoid modifying the test helpers, as there are places (such as calc_oid)
where we want to pass text containing escapes (such as "\n") and have
those be properly interpreted by printf(1).
